Ok, first of all get the datasheets, they are far better than 99% of the tutorials you are trying to find on the web. If you are not satisfied, check this tutorial . They describe the architecture, assembly, external hardware in more palatable words than ATMEL and they make use of the Atmega8 AVR processor as an example. They also have GOOD schematics for the hardware.
In fact, they seem to be happy to give a picture of the whole thing.
As for C programming, the link below is quite didactic as it also teaches C, but it will fill us - C old freaks and 8 bit microcontrollers fans- with good tips.
I had posted another link, but I became aware that it used many deprecated features so I think that the best reference is actually the documentation it self:
Is also a good place to go and play around:
Actually, this is the first site you should check, but the information is not quite easy to find at first grasp, so don't give up. Do like me and try the forums first. Believe me, this is actually one of the few forums around that have posts that can teach you anything on the subject they are supposed to deal with: AVRs. The ARM lists, for example, are full of people rather preoccupied to show their skills than to help.
More of it, I can come up later. Just avoid the hard paths. Go straight to these links given by me.
And of course: http://www.atmel.com
Ok, for now it is all I can give. I still don't have a secure knowledge of the programming softwares to load the hex code to AVRs, they seem to be easy to assembly.