AbsoluteWrite.com has a freebie market listing/links page here with very brief descriptions on type and payment. Absolute offers a much more extensive weekly e-mail market listing via their $15/yr premium subscription service.
Tin House, which pays fairly decent amounts for one-time anthology rights, is presently accepting unagented fiction, nonfiction and poetry for their "All Apologies" Winter 2006 issue:
"ALL APOLOGIES." Fiction, nonfiction, poetry, interviews, profiles, and food and drink writing relating to apologies, confessions, or regrets. Deadline: September 30, 2005. On stands January 1, through March 31, 2006.
Aside from this antho, Tin House's regular reading session for unagented material is September through May. There are a couple of other upcoming anthos listed, including one themed "Un-American" which will feature all non-U.S. writers.
Spicy Green Iguana maintains a good writers market page here, with a range of categories including prozine, semiprozine and small press listings that appear to be regularly updated.