Houghton Mifflin-Math Central
Houghton Mifflin offers good SAT practice and multiple choice questions for each grade level.

First Grade Arithmetic Backpack
This site has over 100 games for basic math in time, shapes, money, addition, subtraction, and more. Activities for K-2.

TeachRkids
This large collection of online activities and interactive worksheets allow kids to practice basic math skills.