I use Safari Books Online as a reference library and to evaluate book before I decide to buy a paper copy, but it doesn't include any Apress books. Is there a better alternative you would recommend?
Edit: Safari Books Online now includes Apress titles which makes it the most complete reference library on the web in my opinion.
With my ACM membership, I get access to both Safari and Books24x7 (this includes Apress).
The selection is reduced from the total offering of those sites (600 in Safari only available to professional members and 500 in Books24x7 available to both student and professional members), but I find it's well worth the ACM annual membership, especially when you factor in the other benefits.
There is a discount for first year members: http://learnmore.acm.org/joinacm5.html
Our local library (nutrias.org) does have ebooks for free also, but I haven't looked to see if they have technical books. In addition, they are term-limited with DRM (yuk).