I prefer to keep the actual patty pretty plain, some salt and a bit of pepper if I feel like it. I love garlic but don't put it on burgers. I need to have the burger patty shaped perfectly (it's easier to buy them premade from a local butcher, still about as cheap as ground beef but they don't fall apart).
I'll grill them on a propane grill once the blood pools a fair amount on the top I flip it, then to finish it I like to smack it a few times with the flipper to get a nice seal on the outside of the burger and get rid of a bit of fat that would soak the bun. Ideally I'll put the burger cheese side down on the bottom of the roll (for those of you in the New York area, JJ Cassone's sandwich rolls are my favorite, pictures on the top left here:
http://www.jjcassone.com/products.html)
The toppings are some fresh coleslaw, a generous slice of a large tomato, sometimes with the seeds and wetter parts removed and eaten beforehand, a nice slice of red or vidalia onion, a thick iceberg lettuce leaf or two, a touch of deli mustard, a well seasoned pickle slice, and some Heinz ketchup (I really do like it more than other brands it seems)
alternatively, it works pretty well for a double burger to cook 2 patties on one side till the blood pools, wipe it off with a paper towel, press some blue cheese or whatever filling you like into it, then attach the 2 patties and continue to cook. I prefer only one patty as I put plenty of other things on, but I do this for others who like stuffed burgers.