A coworker sent me this link recently: www.nerdbooks.com
This company sells most of the major technical books out there, and is often cheaper than Amazon and other rivals. The big perk for me is that they have a location in Richardson, TX where I can pickup the books and save on shipping. The net effect is a good 20% savings per book!
At my normal book buying rate, that would save me at least $200 per year! Woohoo!