Grilled, usually with only salt & pepper. Sometimes I like to put some blue cheese or gorgonzola inside the burger before cooking.
As far as dressing, I like lettuce, tomato, grilled onions and a toasted bun. Sometimes avacado.
As far as favorite restaurant burgers- Steak & Shake, In & Out, Wendy's, Red Robin, the Squeeze Inn in Sacramento and Fuddrucker's.
I remember a great place for burgers in Austin on Guadalupe called G&M Steakhouse. Anyone know if it's still there?