XCode 4 is the best IDE I've seen so far (Disadvantage: only on MAC).
Visual studio 2010 is also great (Disadvantage: only on Windows).
Eclipse 3.7 and NetBeans 6.9, I consider them both at the same level of awesomeness. I use them mostly for JAVA and Python related projects. (Disadvantage: they are slow compared to XCode and Visual Studio + NetBeans is now Oracle

).
The IDE I use the most is GEdit. It is simple, light, fast and awesome at the same time. I use it with some plugins for auto-completion, smart spacing...etc
At last, I cannot forget VI the editor that always save my ass on the slow Lebanese connections when I'm working over SSH.