The UNIX Programming Environment [Kernighan, Pike] is a great companion to the K&R, and a cute little retro read. You can get em used for around $1 (mine cost $0.85).

Some others:
C - A Reference Manual 5th ed. [Harbison, Steele]. The CARM is a great book for absent minded geeks like myself, who easily remember complicated topics but tend to forget the simple ones.

Advanced Programming in the Unix Environment 2nd ed. [Stevens, Rago] (aka The Dilbert). The one that gets used. Stevens is to UNIX what Elvis is to Rock and Roll. This book is but one of several that prove it.

I still have an old magenta coloured 1rst ed. It and the K&R were the first books that really enabled me to move beyond C64 Basic... lol.

It is a terrible book for beginning and intermediate C++ programmers. It is however, a great book for a highly experienced programmer who is writing library code. It is also *the* most exhaustive treatise on C++ language semantics that I know of. IMO: A daunting book for a daunting language...