Purple Math
Purplemath: Simplifying With Parentheses
Explains, with worked examples, how to simplify expressions which involve parentheses and variables, including how to take a negative through the parentheses.
Doina Popovici
Math Play: Properties of Addition Soccer Game
Score goals as you answer questions about the properties of addition.
Math Aids
Math Aids: Properties Worksheets
Great resource for learning and practicing the different properties of mathematics. Math worksheets are printable, may be customized, and include answer keys.
Mocomi & Anibrain Digital Technologies
Mocomi: Addition and Subtraction of Integers
Explores the commutative, associative, and distributive properties of integers, and rules for adding and subtracting them.
Other
Chili Math: Basic Number Properties
Overview of the four basic number properties with examples.