Check out cheat-sheets.org for a metric ton of condensed knowledge on many aspects of software development. Best part is, it’s free! You just need to register with your real email address. I realize I sound like I’m being paid to say this, but it is very useful for picking up new skills quick, and it is free. Enjoy!
I just purchased two pretty good books for less than $5 each shipped. They are …
Indeed you can get newer versions of these books with updated content for 10 times more. But for the money, they are a steal.