The GNU g++ compiler is one of the highest quality compilers out there. It works on most Unix and Linux systems.
Cygwin (http://www.cygwin.com)
Cygwin is a Unix-like programming environment for Microsoft Windows systems; it includes a copy of the g++ compiler.
Borland C++ Builder (http://www.borland.com)
Borland supplies a free copy of the command-line version of their compiler. This is a stripped-down version of the integrated development environment they sell commercially. This is one of the best compilers for the Microsoft Windows environment.
