My procrastination today ended up with me making a Language plugin for Notepad++ that does syntax highlighting for OFP's language.
It recognizes all commands, all Moves, all Objects, all Weapons (incl. ammo, fired & muzzles), all vanilla eventHandlers, all arithmetical functions, comments, GOTOs, and local variables. I can't get it to recognize global variables though, so those will just remain black.
I have attached the file below. It is in .xml format, but you'll have to unpack it from the .zip file
Go to: Language -> Define your language... -> Import -> [select the "SQF.xml" file] to import it into your copy of Notepad++,
then click Save As...
Once you have imported it you can manually choose the language by: Language -> SQF OFP (or whatever you've chosen as the name) to force Notepad++ to use it on your current document.
Once you import it into Notepad++ it should automatically associate with .sqs and .sqf files.
It is written for Operation Flashpoint. I don't play ArmA 1, 2 or 3 so you'll have to correct any differences yourself.