Gotta love* Safari Books Online.
Every book I was about to buy this afternoon, I find I already have**. It's not the first time, either.
No*** Kaner, no Bach, no Whittaker, no Weinberg, so I still need my library. But for everything else**** – from visualising data to Ableton Live, from Python to a guidebook for a 2-versions-old iDVD, there's Safari.
* I agree that it has a frustrating interface, clunky search, single-source issues, is slow for page-flipping, and the 'tokens' make me cross - but I can read those books right now. And there's no new money to find. And I can search. And copy/paste.
** Or, rather, have access to, while I'm online, while my subs continue, and while the service yet lives.
*** I understand the reasons for all these authors not being on SBO, but pure-testing books are generally under-represented. Use this to see the books in the Testing and Debugging section.
**** Of a technical bent.