After reading my book "Publicity on the Internet," Klaus Schallhorn designed two filters for finding out what people are saying about you in newsgroups and mailing lists. Called newsBot and mailBot, they run on Linux, Solaris and Sun only (for now).
University of Maryland's collection of links to information filters. A good place to find and try various Internet filters and news-gathering services.
Infoseek allows you to search the web, Usenet, and certain news summaries. You can also search for e-mail addresses. Their personal news service lets you store search criteria in order to have a custom homepage whenever you visit InfoSeek.
Use AltaVista's link query to find out who has linked to your web site. The format for the search is "link:URL" where URL can be all or part of the address for the web page.
Scott Southwick's humorous and useful archive of information about what constitutes "net abuse" and what people can and have done about it. Includes spam recipes and remedies.