I like things hot and serve these up quite often.  If you have a favorite sauce but would like to make it hotter, you can do a couple of things.  Add some cayenne pepper or habanero powder (just dry some habaneros and crush them).  You can also add a variety of hot sauces, but make sure the flavor of the hot sauce does not ruin the flavor of the BBQ sauce.  One such hot sauce I keep around is Belize Hot...it has lots of heat but won't throw off the flavor of the sauce.