Here are some fun learning web sites I have found to help my kids out.
Starfall (helps with phonics, letter recognition, reading, and has a lot of fun games)
Timez Attack (helps with multiplication)
Coloring Pages (different learning worksheets for preschoolers)
The Math Worksheet Site
Fun Brain (learning games)
Poptropica (a fun geography, mission solving type of game)
I would love to hear about the great web sites that you have found for your kids, especially for math. Leave them in a comment.