MMathboard is very good, you can set the parameters very low and begin practicing math facts. I also like the zaner-bloser handwriting app to practice writing letters. I also grabbed a free flashcard app, and began using that for sight words (which is more Kindergarten, but it never hurts to start early).
Game wise my little ones have enjoyed cut the rope, monster ate my homework, the Disney where's my water one, and about a million others. Also one called puppet pals where they make their own animated type stories with voice overs.