Awesome

gedit-GAS-x86_64-highlighter

This is the greatest assembly language of All Time (gedit port)

This is a port of my GAS x86 highlighter for Sublime Text. More information can be found there. Highlights GAS (AT&T) x86 and x64 code.

Take the .lang file and drop it into ~/.local/share/gtksourceview-3.0/language-specs/, then open Gedit.