About.com C++

Lots of links to other sites

Anjuta Integrated Development Environment

For Linux

Code::Blocks

IDE that can my used with any compiler but it comes with MinGW/GCC

CPlusPlus.com

CProgramming.com

Dev-C++

Eclipse

Eclipse C/C++ Development Tooling

C++ IDE for Eclipse

Intel C++ Compiler

For Linux

Microsoft Visual Studio Express

For Windows, contains C++

NetBeans IDE - C and C++ Development

For Windows, Linux, and many other platforms.