I've found a GREAT way to cut my brownies - first, before I even put the batter in the pan, I line the pan with foil or wax paper so that there is enough overhang to pull the brownies all the way out of the pan (Alton Brown does this).
Once out of the pan, use a non-stick pizza cutter (mine is by Farberware) to run through the brownies! You'll get nice clean lines and no mess in the pan.
If you can read this, thank a Teacher.
If it's in English, thank a Veteran!