The letter C! omics! On the web!
Naturally, we're going to start with our own Planeswalker comics. These are written by the Magic Creative Team, so they're canonical. And they're painted by real Magic artists.
Pro MTG Online : Hands down, the best-drawn MS Paint comic you'll ever see. It's also funny. And have you noticed the secret message in each comic?
Tapped by ManaNation.com : This story-based webcomic is still just getting started, so there's still time to jump on board and learn who the characters are.
XMTG : Also hosted by Mananation, XMTG combines stick figures and text to create humor.
5ColorControl : a relatively new webcomic, updated on Friday evenings.
Lotus Cobra is Evil : MTGColorPie presented fourteen episodes of this hard-to-describe comic created by House of Sixten from October 25, 2009 through January 31, 2010. It's adorable!
This section wouldn't be complete without reference to a couple of the webcomics that have gone by. This is not a comprehensive list, since webcomics frequently flicker in and out of existence faster than the human eye can perceive. These are the ones that lasted. And then stopped.