Fun Brain http://www.funbrain.com/
Free reading and math materials: http://www.starfall.com
Great practice for 1st graders: http://www.internet4classrooms.com/skills_1st.htm
Max's Math Adventures http://teacher.scholastic.com/max/index.htm
Addition Flashcards http://www.aplusmath.com/Flashcards/addition.html
PBS Kids http://pbskids.org/
Author Jan Brett's website! http://www.janbrett.com/games/games_main.htm