It's a favorite In our house, too!

Mashed- DH's favorite
Riced- great for paella to Asian stirfry ices or fried rice. Used for a jumbalaya over the weekend
Popcorn- this is basically just super roasted. It tastes great, but doesn't remind me of popcorn, I'd suggest calling it roasted cauli to avoid being disappointed.

A few more ideas: you can purée to use potato soup base. For example, you can make a New England clam chowder. I bet a loaded baked potato soup would be great, but I have only done this technique with clams, so far.

Slice the head all the way through to make long, skinny "steaks" then roast. These make a lovely presentation. I use evoo, sea salt, garlic, and then top with parsley or chives.

It also makes a nice addition to crudités platters. It is sturdy and holds up to dips well.