I have been a fan of all kinds of comix art as far back as I can remember. Here are just a few sites I highly recommend.
Comics.com

hosts a bunch of comic strips, some old, some new. You can browse for free, or pay a very reasonable sum to have your favorites emailed to you daily!
Ucomics

is the same deal as Comics.com, above, but has lots of OTHER strips. Yes, I am a happy customer of both!
Homepage for the Arlo and Janis strip

The artist updates this 4 or 5 days a week, adding interesting, friendly commentary and a few older strips as a bonus. He has a style that makes you feel like a friend, so I am linking to him as a friendly favor!
Girl Genuis, by Phil and Kaja Foglio!

Out of all the online comic strips, and yes, there are MANY worthy ones, THIS is my favorite!
Sinfest

Wacky. Wicked. Weird. God is one of the characters, and so is The Devil. A must see!
Cartoon Brew blog

VERY interesting stuff about the animation art field, containing breaking news and historical notes. Anyone with any interest in any aspect of the comic/animation art field would enjoy reading this one.