Poker - it will take you a few months to build a bank roll and to actually learn how to play well, but $10 per hour is pretty easy to achieve.
There are lots of guys making $20 to $40 per hour playing poker - and no taxes taken out either.
Technically it is illegal in the U.S. but it still goes on.
On top of playing online - at the age of 19 - you should be able to find some home games or campus games to get in to. Sharpen your skills and these could be worth $50 to $500 a week depending on the level of the game(s) you can find.
www.twoplustwo.com
www.pokertracker.com
Pokerstars is one of the most popular and "fishiest" sites. Limit Hold'em is a good way to get started - you'll learn pot odds and outs very quickly.
No Limit cash games is where it's at now though.
Books for learning - anything by twoplustwo publishing is excellent, everything else is crap. Anything Ed Miller has authored is worth it's weight in gold. David Sklansky is an incredibly source of poker knowledge but he is unable to relate the material to the everyday person. Ed Miller started out at the micro limits and conveys his knowledge very well.