Safari Books Online  is an online bookstore offering everything possible for electronic books on technical issues.

Right off the top, it is not cheap. I have the advantage of a Corporate License through my work. But if/when i should leave, I plan on buying a subscription.

For instance, these searches:

UML (Unified Modeling Language) - 963 Books
.NET - 1744 Books
CSS - 1278 Books
Apache - 1500 Books
Flash - 1000 Books

These are top line books from the likes of O'Reilly, SitePoint, New Riders, Sams, Macromedia Press, Que, Adobe Press...

As these are the top books, just electronically you can open any chapter of any book to find what you want, you can read them online and you receive tokens monthly that allow you to download the book in PDF format to keep. Each book can be added to a favorite list as well. Have a problem with something your programming? Just go there, look up a book you think will help you and solve the problem. If the book is helpful, make it a favorite.