I'd look at those modules that interest me, either because I use them a lot, or because I'd have ideas about implementing similar functionality myself. Since going through someone else's code is not always obvious, extra motivation is important ;-)
A very important criterion is the author, you can get clues on "good" authors by hanging around on Perlmonks and reading posts by various people. Many nice posts are written by people who happen to have authored useful/well written modules as well. I'm not going to name anyone, just see for yourself.
Just my 2 cents, -gjb-