My every-day strips:
Sluggy Freelance, one of the oldest and best.
http://www.sluggy.com/
SinFest, fantastic mix of blasphemy and pimp culture.
http://sinfest.net/
PvP (Player vs Player) , an hilarious daily about the staff of a PC games magazine.
http://www.pvponline.com/
Penny Arcade, one of the greats, but only has a new strip every second day.
http://www.penny-arcade.com/
Demise presents Boomslang, a new one by the guy who used to do Demise.
http://www.demisecomics.com/
Diesel Sweeties, great fun.
http://www.dieselsweeties.com/
explodingdog, though Sam's only putting up new images once a week or so these days.
http://www.explodingdog.com/
This Modern World, by Tom Tomorrow, I read this one every monday when it comes online. The best political cartoon in history.
http://www.thismodernworld.com/
User Friendly, which used to be excellent, but has sunk into nerdy navel-gazing lately. Pity.
http://www.user-friendly.org/
Other strips which I have read a bit but never read all of the archives, so don't read every day:
Calvin and Hobbes online, which is being put up day-to-day in original publishing order.
http://www.ucomics.com/calvinandhobbes/
Dragon Tails, very cute, very funny, and very original, but I never finished the archive.
http://www.dragon-tails.com/
Non Sequitur, the hilarious newspaper strip, new one online daily.
http://www.non-sequitur.com/