Starfall - letters, letter sounds, word families, learning games
ABCYA - reading, math, science, social studies, art, etc. GREAT site!
EPIC Books - books that your child can read or listen to someone read to them! Sign up with your email address.
Cool Math Games - more math games that are fun.
Fun Brain - fun games for learning
PBS Kids - all sorts of learning games, videos, activities
Go Noodle - exercise through dancing, yoga, olympic games, silly songs, etc.