Agree. Why in this day and age I need to fire up an external tool to look at diffs is beyond me. I appreciate the external tool exists (for times when I'm NOT in my editor/IDE to begin with) but I'd rather it was all baked in.

Even if it git or another scm wasn't available - just a diff of changes since the file was opened in the editor...

If you use emacs, this is a good reason to use Magit. Your diff is just a "C-x g" away.

http://www.emacswiki.org/emacs/Magit