here is my second plugin (first was Indent XML) for Sublime Text. It's called ChangeTracker and it highlights changes made in file since last save. Also it allows to navigate through all the changes made.
Here you can watch short (about 1 min) demo - YouTube
Plugin now on github - https://github.com/alek-sys/ChangeTracker
Hope that it will appear in Package Control soon.
P.S. I see the obvious way for this plugin to grow - highlight not unsaved changes, but uncommited changes (for git / hg / etc) If you have any good ideas or want to take a part in development - you are welcome