Compilers

The Symantec C++ 7.21 and 7.50 are often overlooked. They are the new incarnation of Zortech C/C++ and offer several features that are not provided by BCC or VC. The version 7.5 can be had for less than $70 and is a full development system. We enjoy ZTC and SC and use for several programs that only they can support.
This compiler is a steal!!!
NOTE:Symantec no longer supports this product, but it is still excellent. Find it and buy it!

Micro-C is a multi platform cross-compiler that runs in DOS. With the ~$99.00 price you get the full C source for the compiler, libraries and utilities! Micro-C Home Page

GNU and all of it's offshoots (Ada, Pascal, etc) are excellent "free" compilers, front ends and tools with full source code! For the 80x86 versions start the search here.. DJGPP Home Page

Here is the main place to find FORTH and derivitives. Many free with full source code. Forth Page.

Borland C++ 5.5 FREE!

Here is a unique tool for assembler on 80x86 type machines.
Worth a look. Terse - Assembly Language Tool