Donald Catto wrote:
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"The most complete (and concise) reference I'm aware of is 'C - A Reference Manual' by Harbison and Steele."

Given its depth, H&S is generally recognized as being a better "reference" than K&R, as it goes into more of the gory details about C. Its additional benefit is that it deals with and contrasts traditional C (original K&R), C89 (what most of us use now) and C99 (no '51 implementations available yet to my knowledge). Also, not that most of use care, but it shows how to write C++ compatible code (i.e., code that can be used as C or C++).