My favorite is a burger with swiss, grilled onions and mushrooms, and sour cream. I don’t make these nearly often enough!
FWIW, this thread has inspired me to make cheeseburgers for dinner tonight! 
Fortunately, since it’s been snowing like mad since early this morning, we were already in possession of some decent all-beef 1/3lb patties in the freezer, a bag of whole wheat hamburger buns, a couple different kinds of cheese (no Swiss, alas!), A-1 sauce and pickle chips. We even have some frozen French fries. Chill some fruit, and dinner is easy and tasty!
Oh, we have bacon, too. Mmmmm.
I’m simple when it comes to burgers, cheese (I like swiss the best, but I’ll take whatever’s on hand, Amercian, cheddar, provolone, etc).) bacon, some onions, and some pickles. I leave the ketchup and mustard off more “gourmet” burgers, but if it’s a backyard barbecue, throw 'em on. However, TGI Friday’s has introduced me to a new favorite topping. Their Cheesy Bacon Cheeseburger, has a fried circle of provolone on top. Delicious.
We used to have a restaurant in town called Flakey Jakes…a ‘build your own burger’ place, sort of like Fuddruckers but with a much larger selection of toppings to choose from. As I recall, my preferred burger was along the lines of:
Cheddar and Jack cheeses
bacon
carmelized onions
shredded lettuce
olives
barbecue sauce
American cheese, bacon, grilled onions and 2 thin patties.
I went ahead and put everything I like on my burger, even if I might not want them together. Specifically, I think that mushrooms woul be sauteed and have melted Swiss on them, and that’s it besides burger and bun/toast. Everything else would only go on if the mushrooms were omitted. I also like Colby and colby jack cheese.
The way the poll is set up, I don’t think you can tell what I voted for, so I’ll include it below:
[ul]
[li]Swiss cheese [/li][li]Monterey Jack[/li][li]Mozzarella cheese [/li][li]some other cheese [/li][li]Bacon [/li][li]Onion (cooked) [/li][li]Lettuce[/li][li]Tomato [/li][li]Mushrooms [/li][li]Ketchup [/li][li]Mayonnaise[/li][/ul]
Bacon, onion rings, egg, grilled jalapenos, provolone and peccorino (sp?) romano chees, dressed with miracle whip, mustard and cholula hot sauce on a grilled ciabatta bun.
Now I don’t feel so bad about my cholesterol level.
Looking over the poll results so far, one might conclude that people most favor a BLT crossed with a hamburger.
You forget the A1 steak sauce. It makes a hamburger a steak burger.
Beef patty, raw onion, lettuce, tomato, jalapeño peppers, bacon, and chili on top.
No ketchup, no mustard, prefer dill pickle on the side not in the burger itself, no mayo.
Preferably on a hard roll like a kaiser roll, that won’t turn to mush from the chili.
Yeah, just writing that, I could feel my heart slow down a bit. 
Whenever I get fries, I ask for Tabasco, because ketchup mixed with a liberal amount of Tabasco is a fantastic fry dip. Last night they only had Texas Pete (fuckin yuck) and Sriracha, so I tried out some hot cock sauce on my burger. It was tasty!