The best C book I've ever seen is "The C Programming Language" (ansi C) isbn 0-13-110362-8
not cheap but tells you whats happening in a readable way v.good for pointers. Deals with the C langauage rather than all the library functions which most likely are not required for micro controllers. As far as ansi this is just a standard which most compilers default too , HP unix compilers seem to default to the K&R variant but it's all C and the best one is always the one you know best. One good thing about ansi is that it checks function parameters which can be very handy.

hope this helps.

Paul