I actually just wrote a blog about the webcomics that I look forward to reading the most and a little explanation for each:
http://thesoftcorenerd.today.com/2009/07/29/introductions-and-webcomic-round-up/The webcomics I mention include
Penny-Arcade
Joe Loves Crappy Movies
Dinosaur Comics
Dr. McNinja
Saturday Morning Breakfast Cereal
Kate Beaton (Hark! A Vagrant)
A Softer World
Octopus Pie
Anders Loves Maria
Pictures for Sad Children
Of course, I'm excluding some really awesome webcomics that are out there, and that's probably because I either haven't read them or just have a different excitement level when I check their updates (QC included).
In regards to finding other good webcomics, I do what rynne suggested and check out the links from my favorite webcomics. It seems that the really good ones get linked all the time, so I tend to check those out if I haven't already.