C

256-Color VGA Programming in C
VGA basics, lines and shapes, bitmaps, mouse, double buffering, page flipping, and unchained mode. All examples have code provided for Borland C, Turbo C, and DJGPP.
http://www.brackeen.com/home/vga/

Pacific C
Freeware C compiler for DOS from HI-TECH software.
http://www.htsoft.com/products/compilers/PACIFICc.php

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/