Caramelized onions are a lot of fun to mix into different dishes. I put them on steaks, mixed into breads, and they would be great in the French Onion Grilled Cheese that's been going around Pinterest.
I used my small crock pot and fit only 3 large onions inside of it. Put in a drizzle of olive oil, set to low and just let it cook away. Mine took about 8 hours on low to get super sweet. The first bite I took, they tasted like apples. I waited to salt them til after they were nice and brown.