Best options for a beginner?

Alright, I'm looking for a christmas gift for my younger brother. He's become very interested in poker the last couple of years, plays with his friends pretty often. He's 15, and I'm not sure how serious he wants to get about the game.

I'm looking for something which provides a good introduction to theory/strategy, but nothing too complicated. I already have Super System/HOH 1-2/LLHE (lee jones)/and 4 of the Sklansky books, as well as Andy Bellin's 'Poker Nation' and 'Positively 5th Street' if he's interested in reading any of those.

Just looking for a good starter book, maybe something that covers more than just Hold Em, as he claims to play Omaha pretty often. Thanks.