Cool Math
Coolmath: Coolmath4kids: Printable Flash Cards
Find here flashcards for addition, subtraction, multiplication, and division for printing off and coloring.
NumberNut
Number Nut: Addition: 2 Digit Numbers
Learn how to add double-digit numbers in this lesson complete with examples, rules, and vocabulary.
Books in the Classroom
Carol Hurst's Children's Literature Site: Computation and Picture Books
This sample chapter from Hurst's book Picturing Math is an excellent resource for using picture books and activities for learning computation.
NumberNut
Number Nut: Subtraction: 3 Digit Numbers
A brief lesson on subtracting from three-digit numbers that includes detailed examples, rules, and further explanation of borrowing.
Arcademics
Arcademics: Canoe Puppies
Canoe Puppies is a multiplayer math game that allows students from anywhere in the world to race against each other while practicing adding two-digit numbers!