Since Beladonna already started a thread about newspaper comics, and I think online comics would be off-topic, I thought I'd start a companion thread. Here are some of my favorites:

• Angst Technology A less-known must-have for geeks, about a crazy game-software company with a real web-monkey, IT ninjas, etc. Definitely my favorite online or off.
  
• 9 Chickweed Lane Sort of generic "slice of life" stuff, but often with that visual originality I look for.
  
• Doctor Fun One of the oldest online comics; Far Side style, single panel (usually).
  
• Freefall Human-like aliens and robots, just generically well done.
  
• Kevin & Kell Animals this time, but technically savvy ones; a very well developed and original milieu.
  
• Loose Parts Another one of the better Gary Larson wannabes.
  
• off the mark Ditto (hey, I'm a sucker for that stuff).
  
• Sinfest God and Satan appear frequently, along with a more down-to-earth regular cast - a little sexy, lots of pop culture.
  
• The 5th Wave Another geek must-have; weekly, single-panel, Dilbert-ish.

Lastly, here's a post on my website with some of my personal favorite examples from some of the above.

Edited out unauthorized link.

I'm a fan of Red Meat.

I second Quarkie's recommendation of Red Meat and would like to add the faaabulous This Modern World by Tom Tomorrow!


(Speaking of Gary Larson wannabes, let's not forget that Gary Larson was himself a B. Kliban wannabe!)

Pearls Before Swine

Without a doubt, one of my favorite comics, although angst tech is swerving into the lead. The first several where they're searching for a webmaster are hilarious!

Thanks for the pointer to Red Meat - it's hilarious! I SO want the glow in the dark t-shirt!

Bug eyed Earl is hilarious!