Weeding the Library Collection
http://www.wmrls.org/services/colldev/weeding.html
Links to some of the best known weeding sites on the web, including a look at the CREW method from the Texas State Library and Archives Commission; also links to another online tutorial from the Idaho Commission for Libraries.

Weeding (Arizona Public Libraries)
http://www.dlapr.lib.az.us/cdt/weeding.htm
Another good introduction and overview of weeding library collections (even though the external links need to updated).

SUNLINK Weed of the Month Archive
http://www.sunlink.ucf.edu/weed/
Although this site is no longer actively maintained, the archives are still worthwhile. The site is also a good example of how a library system can make weeding an ongoing process -- focus on one area each month and list criteria for weeding that particular subject area.