Ever since I discovered it, D.C. Simpson's Ozy and Millie has been one of my very very favorites. The influence of Bill Watterson's masterpiece Calvin and Hobbes is apparent in this anthropomorphic series starring a pair of precocious fox-children, serene straight-man Ozy and plucky troublemaker Millie, as they ponder school, bullies, politics, zen, and the meaning of life. It's wise, irreverent, funny, and brilliant. Start at the beginning of the archives and read through -- it's the only way to go. You can also check out House Rules, a selection of O&M strips in color, or I Drew This, D.C. Simpson's political cartoon series. He also has a livejournal.
The Girl in Black is a very nice strip about the titular darkly-clad girl and her hirsute boyfriend. I love the drawing style, and the characters are likable and ring true. A pity the comic isn't in production any more...I'd love to see more.
Little Dee is a traditional newspaper-style comic strip, about a little girl who is adopted by a family of animals. Cute.
Questionable Content is another of those day-in-the-life comics about a group of mildly angsty twenty-something friends. This one is pretty cleverly done. Oh, and there's also a pet robot.
PhD is Piled Higher and Deeper, a "grad student comic strip" with massive archives stretching back almost ten years. From to writing the perfect thesis title to stealing food from seminars, It's the entire graduate-school experience distilled into comic-strip form.