I come across lots of good reports, white papers, etc. that have a lot to say about some aspect of green computing. I thought I would post a bunch en masse.
Analysis of the Impact of Open Source Software - A good read about where OSS is giong and how much you can save by implementing it.
Sun's position paper on sustainable computing - Sun has the best strategy going on sustainable computing. Even you you don't use their equipment, it's a must read. You probably will soon.
Thin Clients - several white papers on thin clients.