FYI Humble Bundle has a collection of Electronics books on sale humblebundle.com/books/make-arduino-and-raspberry-pi

some of the titles include" make sensors, avr programming and make bluetooth.I have read all 3 and can recommend them.

@SteveRobillard Thanks for that! I took a look over the list earlier and it looks like a good buy for the price ($15 for the lot).

@goobering Yeah, most of them will cost that much alone so even if you don't need all of them it is a good deal.