I've been working with Ryan on identifying sets of objects (5 and less) without counting. For example, I'll show him 3 fingers, or 4 apples and ask how many there are. If he starts to count them, I'll ask him if he knows how many there are without counting. This is part of our new math curriculum, Right Start Mathematics.
I've been taking it one step further with a really simple math game. I place 5 'magic beans' (glass pebbles from the craft store, or actual beans) in one hand. I have him close his hands and I transfer a few beans to my other closed hand. When he opens his eyes he can see how many beans remain in my original open hand. I ask him how many magic beans disappeared. To figure it out he has to not only determine how many are in my hand, but then try to compute the difference between that number and 5.
Of course, he loves to take a turn making the beans 'disappear'.