While I was checking books which I would like to buy, I found these two webpages which share literature about C/embedded/signals.
Keil embedded bookshelf [keil.com/books]
I had to ordered another two new books which I have not read yet, ARM assembly language and ARM system developer's guide. I can't wait to read them.
AVR freaks - Online C books and Tools [avrfreaks.net]
Rich list of many tutorials, books mostly for C lang, AVR related.