For the basics - give me a burger w/ bacon on it, basically. Can't go wrong w/ bacon, IMHO.
Ketchup, BBQ sauce, or teriyaki for me works well for sauce thrown on top.
Some of my fav. burgers:
Empire State Burger @ RF O' Sullivan's (Somerville, MA) which is a burger with a sausage on top.
I've had at few places a burger w/ short-rib on top, which also was delicious.