For fluency (addition/subtraction, multiplication and division facts), my kids love Big Brainz. They have a free version and deluxe version (deluxe version only for mult. and division). It is like a real video game where they run through a dungeon, ruins, volcano, etc. beating monsters by typing in the correct answers on time. My 6 year old, who had no interest whatsoever in flashcards, asks to play the game a few times a week and he has almost mastered division. He has been playing for a few months so it's not like he was into it for a couple days and then lost interest. My 7 year old daughter likes it as well, but isn't quite as into it.
