Eclipse Ganymede
If you've never looked at Eclipse and you work with multiple programming languages or multiple platforms, take some time to try Eclipse.
Be prepared. Eclipse is a large, complex tool, and you won't grok it if you invest only 15 minutes. In addition to being large and complex, Eclipse's roots are at IBM, and it's big in the Java world, so there's a bit of "Blue-Speak" and "Enterprise-Speak" to deal with at times (and, of course, XML).
Most IDEs come with built-in “support” for lots of programming languages. Although for a lot of them, support means it colorizes your code. Eclipse is a bit different. It doesn't come with built-in support for many languages, or any, depending on the version you download. Support is provided via Eclipse Plugins. And normally, “support” means more than just colorizing your code. You usually get something that understands your language. It can show you an outline of the functions and data in your code; it can help you refactor code; it can show where something is defined, and it integrates with the language's debugger.
Eclipse is not without its annoyances. Perhaps the most annoying is that it's only an IDE and not a text editor. Of course it edits text, but it's not a general-purpose text editor. If you want to open a file that's not part of a project, it's a bit cumbersome. There's no filesystem browser, and the open dialog doesn't remember the directory that you used last time. And, if you don't have a plugin for the file type you open, you don't get any code colorizing. So, you often end up using Eclipse for your “projects” but then using another text editor to look at files that aren't part of your project.
If you develop only C++ applications for KDE on Linux, or only XXX applications for YYY on ZZZ, there might be a better IDE than Eclipse. However, if you use multiple languages and/or multiple systems, and you want to use only a single IDE, there's no better IDE than Eclipse. And, even if you use only one language on one system, Eclipse sets the bar pretty high.