CardMaster Conflict -
http://www.cardmasterconflict.com/
It's a free and fun CCG, with creations from the mind of Mark Shallow (creator of
ADVENTURERS!,
Antihero for Hire and more), featuring cameos of various other webcomic artists and in-depth player involvement. I've played over six thousand matches, personally, so I thought I'd give it a proper shout-out here.