uhm... what about *drums* SED?
o.O

Notepad++ is a good general purpose editor

Also you could use Eclipse and install some C plugin,
and make some buildscripts to run the engine.

I like SublimeText 2 very much

Visual Studio 2010 (Express C++) with some changes in project settings

That's an interesting tool. How do you integrate it with GS? Do you have to create a custom build system for that?

example for "Image Factory"

image_factory.sublime-build

"{
"cmd": ["C:\\Program Files (x86)\\GStudio8\\acknex.exe", "C:\\Users\\Marian\\Documents\\My Dropbox\\Projekte\\Image Factory\\main.c", "-diag"]
}
"

IF you just want a "build open file" [sed's blue arrow] you can use $file .

I haven't found out how to use a "main" script without creating a special build system yet though

Also, my "highlighting" sucks [just added main structs/variable types to the syntax highlighting of C and called in LiteC] - but well, that's because I am lazy^^

Eclipse CDT

Hehe, no, I spent a lot of time configuring everything. As of yet I haven't been able to properly include acknex.h. If that worked, keywords would be automatically colored. I did get the compilation and running to work, and all homemade code is colored.

Creating an independent 3dgs-eclipse from the base is perhaps a better idea since you can create your own lecturer, but a lot more work too.