You can make a deconstructed Onion Soup sandwich: grill some good bread with some grated gruyere/cheese of choice, could do this under the broil or on a pan. In a separate pan caramelize the onions. Sandwich the onions in the bread with the melted cheese. I think a sprinkling of parmesan mixed in with the cheese mixture would taste amazing, as well as some fresh chopped thyme in the sauteing onions.
Caramelized onions would be delish as a salad topper, with steak as a side or in a steak sandwich, really good mixed in a combination of cream cheese/mayo/plain yogurt for a veggie dip, etc etc.