Cream cheese (can be thinned with a little milk, if you want), mixed with chopped spinach or your favorite herb
Cream cheese with crabmeat, sherry and your favorite herb
Cream cheese with minced, sauteed mushroom stems and your favorite herb
Cream cheese and chopped jalapenos
Cream cheese and pesto
Brie with some minced shallots
Figure on about eight ounces of cheese for a pound of mushrooms, or half that for the 10-oz. packages of mushrooms we seem to get here. You could substitute one of those spiced cheeses (Boursin, Alouette or Rondeli.) 1/3 to 1/2 cup of crabmeat. 2-3 tablespoon sherry. You can’t combine the shallots with the brie, so just sprinkle them on top and let them sink in as the brie melts.
Remove the stems, stuff, and broil for 5-8 minutes. Some people brush the caps with olive oil and pre-broil them a little bit before stuffing them. It depends on what texture you like your mushrooms. If you don’t cook them before stuffing them, they’re easier to pick up with your fingers. If you do, you might need forks. If you use larger mushrooms, like portobellas, you’ll have to pre-broil them. You could also try sprinkling some buttered bread crumbs on top of any of the above.