Useful link:

Artswire.com
Database of cultural resources, art news, international calls and job listings, a program of the NY Foundation for the Arts.

Art Calendar.com
Business magazine for visual artists, includes national calls for entries.

Absolutearts.com
Web guide to international art exhibitions , post press releases for art-related events. Free.

Queer Arts Resource.com
Art and LGBT-related resources are compiled on this beautiful site.

Online Portfolios / Galleries

Art in Context
Low-cost portfolio service.

artnet
Important resource on contemporary art, based in NYC.  Includes links to a huge spectrum of international artists.

Portfolios.com
Portfolios online.

nextMonet
Online gallery and art sales, based in the Bay Area.