What's a good portable game for kids in the car? Ages 8 and 10.

If you ask me, I would have to say either Nintendo's GameBoy Advance (GBA) or DS. I have seen some educational type games for the PSP, but most of those are also out for the GBA and/or DS. Non-educational games will be, by and large, far more suitable in content on the GBA or DS compared to the PSP however. Nintendo has a large number of fun games that don't rely on a violent premise.

You also shouldn't discount PC games, where I suspect you'll have a much easier time finding educational games. There are also likely to be plenty of board games. Something like Scrabble can go a long ways to building someone's vocabulary and spelling abilities.

Reading books is another thing you should be encouraging in your son. It can be just about any kind of book, so long as it was professionally edited. It will improve his spelling, grammar, vocabulary, attention span, and several other cognitive functions. As I recall, around your son's age, I was big into Hardy Boys books. Just as a possible starting point in your search. If he likes them, there are dozens, if not hundreds, of books in that line he could read.