Art Crimes: The Writing on the Wall
http://www.graffiti.org/
A very in-depth exploring graffiti as an art form and as a sociological phenomenon. Many articles and interviews, book and magazine reviews, photo galleries and more.
Art.net
http://www.art.net
Extremely minimalist design that looks like it was created back when Mosaic was the browser of choice, but a lot of good content nonetheless. There are studio sections for a wide variety of artists working media from painting and sculpture to digital media and performance, and even musicians and poets, plus virtual gallery showings, a calendar of art events, and more.
fineArt forum
http://www.msstate.edu/Fineart_Online/
Described as "art + technology net news", fineArt forum is the longest running arts magazine on the Internet. It actually predates much of the web, having begun as a Gopher site in 1993. fAf began as an offshoot of the Arts, Science and Technology Network (ASTN), based in France, but has since been published out of the US and now Australia. A massive amount of content, including back issue archives, and art resources from five continents.
Flightless Hummingbird
http://www-personal.umich.edu/~rmutt/
It's awfully hard to know what to say about this one other than that I find it endlessly fascinating. Described as a pseudo-periodical of art, paranoia, eschatology and fashion tips, it's a strange adventure in hypertext that could equally well be classified under art or creative writing. My favourite bits are the Functionless Form and the legal disclaimer.
MOBA - The Museum of Bad Art
http://www.museumofbadart.org/
"The pieces in the MOBA collection range from the work of talented artists that have gone awry, to works of exuberant, although crude, execution by artists barely in control of the brush. What they all have in common is a special quality that sets them apart in one way or another from the merely incompetent." One of my personal favourites. You will laugh 'til you pee...
Reign of Toads
http://www.rtoads.com/hypertoad/
Web site of an eclectic art/culture/tech zine published in the early 90s. Includes a listing of the four back issues with many reviews and a few articles online and more apparently to come, plus some content towards a fifth issue.
The Surrealism Server
http://www.madsci.org/~lynn/juju/surr/
Among my favourite sites. It's far too easy to get lost and spend hours here. An archive of surrealist writings, bibliography, web resources, surrealist games, automatic writing, critical paranoida, and the especially fabulous Surrealist Compliment Generator - sample output: "Your wit, your teeth, your pasty reflection can but incorporate freely into the powerful surface of a disintegrating mirror set afloat upon a swarm of locusts." You don't want to know how many times in a row I've reloaded that page...