It's seldom boredom that drives me to webcomics - it's stress from work. I try to check each of these webcomics three times a week (usually MWF):
PVPONLINE - a webcomic about the crew behind a gaming magazine.
Least I Could Do - a webcomic about a man struggling desperately not to mature, and his saner circle of friends. Warning - There's some sexual content here, as evidenced by the logo.
Multiplex - a webcomic about a movie theater and the staff that keep it running.
Girl Genius - the continuing adventures of Agatha Heterodyne, the Emperor of Cats, and a number of Sparks.
Giant In the Playground - two webcomics here: Order of the Stick (self-aware fantasy webcomic using D&D3.5 rules) and Erfworld (adventures of an overweight wargaming genius who is transported to a fantasy world with strange laws).