another approach to your old computers is giving them to a group like World Computer Exchange trying to bridge the digital gap by exporting U.S./Can computers to developing countries
http://www.worldcomputerexchange.org/

No matter where you are, there's a great website that offers consolidated resources on where to go to recycle things and what to recycle (especially hard-to-recycle things, like computers and cell phone):  Earth 911 or http://www.earth911.org.  Enter your zip code to find resources in your area.

I've heard some unfortunately sketchy things about our so-called electronics-reycling programs, however. A lot of US companies who so helpfully collect our old computers and gadgets contract with overseas companies, particularly those in East Asia, who lack both the facilities and know-how to carefully process the dangerous chemicals concentrated in things like computer processors and monitors.  I've seen videos of poor rural communities processing these chemicals by burning them down in open-air fire pits -- processes dangerous to the health of the individuals and potentially contaminating the water and air resources of the communtiy as a whole.  Perhaps Umbra can clear this up for us some day.  

I admire the good intentions behind such projects, but have to wonder if it's really benevolent to ship dated computer equipment off to anyone, no matter how "developing" (read: impoverished) they may be.  

Note for instance that GeekCorps does not mention accepting donations of used computer equipment for their work with people living in developing economies.

AlterNet just published an article that talks about recycling old computers and other electronics, and specifically picks on Apple for doing a shoddy job of it.

I have been using E-Tech Recycling for all my electronics recycling needs. They are a 100% local recycler. If you need more information about their service visit their website at http://www.etechrecycling.com