It's been a while since I use a lightweight IDE such as Editplus or UltraEdit (or Eclipse, if you call it lightweight too). But recently I use Codeblock from editing my GLSL. Yes its not the best GLSL editor, but I am pretty impressive by the attention to details they put in it.
I mostly use XCode. My main language is C++. XCode is wonderful. It has the best syntax highlight for C++ as far as I notice. I also perfectly match the OS X environment so you can easily attach Library (or Frameworks) to your program. But there are some Codeblock feature that shock me a lot since I'm comparing a freeware against an IDE made by the most cash company. Here are the attention-to-detail features that I admire the most:
1. Variable highlight through all the current document if you double click a variable. It makes it easy to notice where and what I did to the variable before it reach there.
2. Great Intelisense although it may not work if you did not put your files in the same project.
3. Best syntax highlight for C++.
4. Detects any compiler exist in your OS makes it easier to jump in right away.
There are the big four I can notice by now. If you want to start programming in C++, this is one of the best bet you can have. And the best part is its multiplatform and free! Kinda shock how far Freeware can go!