I'm a pretty classic burger kinda guy. I don't like those burgers with a bunch of stuff mixed into the patty - eggs, breadcrumbs, onion, etc. That's meatloaf. A burger should be meat, salt, and pepper.
But this recipe from James Beard is intriguing.
Blog post:
http://www.tastingtable.com/entry_de...ames_Beard.htm
Recipe:
http://www.jamesbeard.org/recipes/my-favorite-hamburger
James Beard grates onion directly into the patty and uses cream to add richness.