Definitely get Harrington on Hold 'em
volumes one and two, they're kinda the bible for NLHE tournament play.
Definitely do not
get Super System
- one or two. They're fantastic books if you want to play mixed games for high stakes. If you want to play low to medium stakes hold 'em there are seriously a dozen better books you could buy. The hold 'em section (it's basically the same in both versions of the book) assumes you'll be playing for high stakes against weak-tight opponents so don't bother unless that sounds like your regular game.
For my money, I'd get Killer Poker - No Limit
by John Vorhaus as the second book (assuming you count two volumes of Harrington as a single book). It covers both cash game and tournament play and it really encourages you to analyse your own play and identify your own leaks as opposed to just pushing one method of playing.
That's just me though. I've heard plenty of good reviews on the Harrington on Cash Games
books. If you want to play live, Read 'em and Reap
by Joe Navarro is a must (for reading tells
and, more importantly, concealing your own ones- skip Mike Caro's Book of Tells
, Navarro is much better).