For the cheap skates amongst us there is a great resource for those looking to expand their skills, FreeTechBooks.com is a great resource for tech books available freely online all in one location.
The moderators are as careful as can be to make sure they are not violating copyrights and have taken down a few books that made it onto their list in the past. So for guilt free resources on anything from Artificial Intelligence to Electronic Circuits, check them out.
This of course assumes you are one of the people who can sit back with a good laptop and read. Personally, I think that’s what an ebook reader on my phone is for. Though if anyone wanted to buy me a gift, the Sony PRS-505 Portable Digital e-Reader System