I've been using Arduino for awhile and now I'm interested in programming AVR microcontrollers without the Arduino framework.
What is a good reference for beginning AVR programming in C? A book is preferred, but online resources are also welcome.
I'm looking for something that will start with basic setup on a *NIX platform, start with examples and cover a number of core topics. Something similar to K&R, but oriented toward microcontrollers would work well.
(Related question: Linux / Mac AVR Programming Suite?)