Free Geek is a 501(c)3 non-profit in Portland, Oregon, who collects unwanted, second-hand hardware and either puts it to good use in the community or recycles it responsibly. They have been hugely successful in the short time they have existed.

Volunteers accumulate hours there, which can in turn be traded for working linux systems. (Training on these systems count towards these hours.)

Also, this is a great resource for non-profit projects (like community wireless networks!) to get older machines that Free Geek has plenty of (e.g. 486s) to use in their projects for things such as simple servers or hubs, etc. for more info.