I've whitelisted 100 domains from http://www.realcities.com/, which has a list of city sites run by large U.S. newspaper corporation Knight Ridder. None were blacklisted before. About a dozen were already whitelisted. Most are newspapers. These would be unlikely to be used by professional spammers.

http://spamcheck.freeapp.net/whitelists/realcities.sort

Jeff C. -- "If it appears in hams, then don't list it."