Depends what flavours I'm aiming for. Curry style burgers would be nice. Add a bit of ground cumin and corriander into the cooked onions at the start and then maybe some fresh chili for heat later on before you form them. Chinese style burgers are nice. Flashy's made some of them before now with 5 spice etc. and they were accompanied by chinese chili and garlic sauce (not dipping sauce, the cooking kind) potato wedges. Delish!
Hmmm I wonder if you could secret bits of bacon and flat plastic cheese in a home-made burger instead of putting them on top so they ooze when you bite into it.
*plots international cuisine burger making operation this weekend*