Free Math Worksheets
Here you can generate printable math worksheets for a multitude of topics: all the basic operations, clock, money, measuring, fractions, decimals, percent, proportions, ratios, factoring, equations, expressions, geometry, square roots, and more. I have also put together pages that list worksheets by grade levels (see below).
The worksheets are very customizable: you can control the number of problems, font size, spacing, the range of numbers, and so on. The worksheets are generated randomly, so you get a different one each time.
All of the worksheets come with an answer key; however, you need to click the link to the answer key immediately after generating the worksheet, because the answer key is only generated when you click on that link. Because of this, you cannot find the answer key for a specific worksheet later on, should you come looking for it.
NEW! Worksheets for number bonds — available both in PDF and html form.
UPDATED! Seven reasons behind math anxiety and how to prevent it
NEW! Worksheets for long division, basic division facts, and division with remainders. Available both in PDF and html form.
Copying permission: you can freely print and copy unlimited copies of the worksheets for use in the classroom, home, tutoring center—anywhere you might be teaching. If you want to distribute the links or worksheets on a website or publication, please contact me.
By grade levels
PREconfigured worksheets for grade 1 math, randomly generated. All you need to do is click on the links.
You can also find first grade

PREconfigured worksheets for grade 2 math, randomly generated. All you need to do is click on the links. You can also find second grade

PREmade worksheets for grade 3 math, randomly generated. All you need to do is click on the links. You can also find third grade

PREmade worksheets for various grade 4 math topics. Still randomly generated, but all you need to do is click on the links.

PREmade worksheets for various grade 5 math topics. Still randomly generated, but all you need to do is click on the links.

PREmade worksheets for various grade 6 math topics. Still randomly generated, but all you need to do is click on the links.

PREmade worksheets for various grade 7 math topics. Still randomly generated, but all you need to do is click on the links.

Elementary math
Addition of whole numbers and integers, either in horizontal or column form. Have up to 6 addends. Missing addend problems, option of no carrying.

Number bonds are pairs of numbers that add up to a given number. Find readymade worksheets for number bonds from 8 through 15 and a generator you can use for other numbers. Available both in html and PDF formats.

Number charts for counting, skipcounting, multiples. Choose a list
or a chart with numbers in boxes. Choose the counting step and how much
the student fills in.

Basic operations of integers and whole numbers, including operations in columns, long division, and division with remainder, missing addend/factor problems. Control the number ranges easily.

For grades 3, 4, and 5. Includes skipcounting, multiplication tables, missing factors, multiplication algorithm (long multiplication), and factoring.

For grades 3, 4, and 5. Topics include division facts, mental division, long division, division with remainders, order of operations, equations, and factoring.

Change normal numbers to Roman numerals or vice versa. Or, do addition and subtraction problems with Roman numerals.


Tell time from analog clock, or draw hands on clock when digital time given. You can choose the clock image size. Available both in PDF and html form. The page includes both a generator and premade worksheets for grades 13.


Practice converting customary measuring units. Available both in PDF and html form. The page includes both a generator and premade worksheets for grades 27.

Practice converting metric measuring units. Available both in PDF and html form. The page includes both a generator and premade worksheets for grades 27.

Special
... and sample pages from Math Mammoth books, completely free! These aren't scriptmade but contain very varying problems on a host of topics.

A tribute to Whitney Houston... I Will Always Love You

Counting objects, odd/even, addition, subtraction, multiplication, division, currency, comparisons, place values, sequences, games.

Money (various currencies)
Count common US coins or bills. You can choose which coins/bills will be used, and how many coins/bills are shown at most. 
Count common Canadian coins or bills. You can choose which coins/bills will be used, and how many coins/bills are shown at most. 
Count common Australian coins and/or bills. You can choose which coins/bills will be used, and how many coins/bills are shown at most. 
Count common South African coins and/or bills. You can choose which coins/bills will be used, and how many coins/bills are shown at most. 
Count common British coins and/or bills. You can choose which coins/bills will be used, and how many coins/bills are shown at most. 
Count common euro coins and/or bills. You can choose which coins/bills will be used, and how many coins/bills are shown at most. 
Fractions
Worksheet generator for addition, subtraction, multiplication, and division of fractions and mixed
numbers. 
Simplifying (reducing) fractions, equivalent fractions, convert fractions to mixed numbers or vice versa. You can control the ranges of numerator, denominator, and whole number part.

Worksheets for addition of fractions, organized into sections for grade 4, grade 5, and grades 67. Available both in PDF and html formats.

Worksheets for multiplication of fractions and of mixed numbers, organized into sections for grade 4, grade 5, and grades 67. Available both in PDF and html formats.

Compare or order fractions. Many options; you can even include pie images for students to color!

Five different problem types, four of which include visual models (pie images). Available both in PDF and html form. The page includes both a generator and premade worksheets for grades 45. 
Add, subtract, multiply, or divide fractions with this handy calculator.

Decimals
Worksheets for either changing fractions to decimal numbers, or decimal numbers to fractions. Many options. 
Basic operations of decimal numbers, either in horizontal or column form, including long division. 
Worksheets for mental multiplications & multiplicatio algorithm with decimals. 
Worksheets for mental divisions & long divisions with decimals. 
Worksheets for rounding decimal numbers, with various options.

Number theory
Worksheets for rounding whole numbers, with various options.

Worksheets for writing numbers in expanded or normal form, or writing numbers in scientific notation.

Worksheets for exponents, with various options.

You can choose to take square roots from numbers that are perfect squares or not, or from decimal numbers. The more complex worksheets have other operations like addition or multiplication besides just taking a square root.

Worksheets for prime factorization. Easy, medium, or challenge levels.

Worksheets for the greatest common factor and/or least common multiple of numbers.

Ratio, proportion, and percent
Create proportion worksheets with either numerical problems or simple word problems (e.g. speed/distance or cost/amount problems). Options for using whole numbers only or numbers with a certain range or a certain number of decimal digits.

Simple word problems involving ratios, for grades 68.

Worksheets for either changing percents to decimal numbers, or decimal numbers to percents. Or, choose a mixed worksheet that has both types.

Simple worksheets to find percent of number. Control the range or step of percent and of the base number, as well as decimal digits, to make mental math worksheets or more difficult ones.

Problems can be of three different basic types: find either percentage, percent, or the base number. You can choose the wordings of the problems, and control the decimals, ranges, and steps for the percent or numbers shown in problem.


Geometry
Identify the various types of triangles. Classify triangles by their sides, angles, or both.

Identify the seven different types of quadrilaterals (square, rectangle, rhombus, parallelogram, trapezoid, kite, and scalene quadrilateral).

Problems for area and perimeter of rectangles/squares with images, word problems, write an expression for area using distributive property, irregular rectangular areas, and more.

Calculate either the radius, diameter, circumference, or area when one of those is given.

Find the area of triangles, parallelograms, other quadrilaterals, and polygons (pentagons/hexagons) in the coordinate grid.

Find the volume and/or surface area of a rectangular prism, including with fractional edge lengths. You can also make problems where the volume or surface area is given, along with some dimensions, and then you need to calculate either the volume or the surface area.

Students either plot points, tell the coordinates of points, plot shapes from points, reflect shapes in the x or yaxis, or move (translate) them up, down, left, or right.

Prealgebra
Worksheets for writing simple expressions with variables, when the expressions are given with words. For grades 68, prealgebra, and algebra 1.

Worksheets for evaluating simple expressions with variables, when the value of the variable(s) are given. For grades 68, prealgebra, and algebra 1.


For prealgebra and algebra 1. You can control the number of problems, difficulty level, type of expressions, workspace, and more.

Worksheets for linear equations. Includes onestep, twostep, multistep equations, variable on both sides, and more. For grades 69, prealgebra, and algebra 1.


For prealgebra and algebra 1. Graph linear equations and determine the slope or the equation of a line. You can control the type of problems, number of problems, whether a fractional slope is allowed, workspace, and more.

For prealgebra and algebra 1. Plot a given inequality, write an inequality from a graph, or solve various types of linear inequalities with or without plotting the solution set.


Word problems involving constant (or average) speed, time, and distance.

Choose from five operations and parentheses. You can choose the number range used, number of problems, and more.


Solve equations, inequalities, and systems of equations, simplify or factor expressions, and much more with this online algebra solver.

Free online equation editor for teachers. Makes an image you can save.


Worksheets for practicing negative and zero exponents, available both in PDF and html formats.

A list of other websites that offer free worksheets for algebra.

Other math worksheet websites
DadsWorksheets.com  thousands of free math worksheets
This site has over 5,000 different math worksheets from kindergarten to prealgebra and growing.
Deluxe Vectors  Free Vector Graphics
This site is not about worksheets, but is quite handy for students and teachers, as it cointains tons of free vector clipart.
Math Maze
Generate a maze that practices any of the four operations. You can choose the difficulty level and size of maze.
10 Quickies Worksheets
Interesting math review worksheets... with 10 questions per page, but each page has a scenery that kids can color afterwards. A few free samples available.
Worksheets and Hintsheets from AppTutor
Gradelevel specific multiplication and addition worksheets and "hintsheets"—summaries or factsheets with important information about the operation.