The C Book - Complete online version of second edition book by Mike Banahan, Declan Brady and Mark Doran. Popular introduction to ANSI Standard C. - http://publications.gbdirect.co.uk/c_book/
A to Z of C - The non-profit free book on C/DOS/Turbo C programming with 79 chapters. It's available online to view/download. - http://guideme.itgo.com/atozofc/
Writing Bug-Free C Code - Online book by Jerry Jongerius advocates a style of programming based upon classes, data abstraction, run-time type checking, and fault tolerant functions which results in bug-free C code. Sources, Amazon link for printed copy. - http://www.duckware.com/bugfreec/
The C Programming Language - By Brian W. Kernighan and Dennis M. Ritchie, the original (revised) and the best book to learn C. - http://cm.bell-labs.com/cm/cs/cbook/index.html
Simulating Ecological and Evolutionary Systems in C - Book by Will Wilson. The book starts with elementary programs modeling stochastic birth-death processes, slowly increasing programming complexity as the chapters progress. - http://www.biology.duke.edu/wilson/Book/
C Elements of Style - Programming books,information, and columns. - http://www.oualline.com/
C Interfaces and Implementations - Explains the use of various interfaces such as string manipulation and data structure. - http://www.cs.princeton.edu/software/cii/