Eclipse is a popular development platform, kind of more than an IDE. It is based solely around plug-ins and provides a good development environment. At the moment most of its strength is the Java development and its use for embedded systems (see my previous article about SunSPOTs - that used the Eclipse IDE for remote debugging.
One of the projects within it I keep an eye on is the CDT project which is a plug-in for C/C++ aiming to be as strong as the Java development. At the moment it is used a lot for the embedded space, but they want to extend it even further and challenge the
Visual Studio IDEs.
The guy heading up the CDT project Doug Schaefer has been blogging about the progress of the project for a while. In the CDT 4.0 roadmap the plan is to use the Windows SDK and have integrated debugging and the suchlike. His most recent post "Migrating From Visual C++ to CDT" shows the progress the project is making. It is always great to have alternatives and Eclipse certainly could help along that route. Part of the plan is also to add C# support as well from the Windows SDK. At the moment I would not recommend using CDT in lieu of VS2005 for Windows application development but if your toolchain is make based you may find this a better alternative.