99 Ways to Market Your Art - Copyblogger
AdBusters - is a global network of artists, activists, writers, students, educators and entrepreneurs who want to advance a new social activist movement for the information age.
Art cyclopedia - The Fine Art Search Engine
ArtForum - The online edition of Artforum International Magazine.
ArtLex Art Dictionary - Great reference material in art, art history, art criticism, aesthetics, and art education. Definitions of thousands of terms, illustrations, quotations, and links to other resources.
Arts & Letters Daily - ideas, criticism, debate
ArtsJournal - Daily arts news from more than 200 newspapers, magazines and e-publications
ARTS SIGMAA - mathematics and the Arts
http://www.ebsqart.com/ - Self Representing Artists
UbuWeb - a completely independent resource dedicated to all strains of the avant-garde, ethnopoetics, and outsider arts.