I personally use
Notepad++ to write all my scripts and then I go into mplab just for compiling (press F10), even though I know how to run MCC18 out of a batch file.
Notepad++ supports about 30-ish different languages and does highlighting and colorizing of text depending on the file extension. It supports multiple documents open in the same window, split views on the same or different files at the same time, and collapsing of structures (e.g. any statement inside {'s can be collapsed much like a tree view). It also has a function browser built in (shows all the functions in the file), and can run an executable of your choice off the F5 key.