OK, I've tried a bunch of different vegetarian combinations and I must say that this has been an eye-opening exercise for me. It has forced me to try some things that I would have never considered putting on a pizza. Prior to this, the only pizza that I would ever make without meat is a cheese only one.
I tried several of the combinations suggested here as well as a few of my own variations of them.
I have used smoked mozzarella and smoked provolone on several veggie pies and they are marvelous. As I think someone mentioned, it kind of gives a bacon-like taste, especially with some EVOO.
Some of my favorites have been:
Smoked provolone, caramelized onion, Brussels sprouts, EVOO, sea salt. This makes two ways that I like Brussels sprouts now.
Smoked provolone, caramelized onion, kale, EVOO, sea salt. Same as above except with kale instead of Brussels sprouts. I've always thought of kale as a garnish. I think that this is the first time that I've actually eaten it and it was very tasty this way.
Fried breaded eggplant, mozzarella, Pecorino Romano, red sauce. Wow! I enjoyed this a lot!
Asparagus, artichoke hearts, sauteed onions, spinach, red sauce. The one slice that I had was great. My wife couldn't get enough of it.
Green tomatoes (thinly sliced), EVOO, minced garlic, sea salt, black pepper, smoked mozzarella, Pecornio Romano. My Aunt supplied me with the green tomatoes from her greenhouse. This was my own experiment. Delicious!
I haven't had a chance to try any of the faux meats yet.
Thanks again everyone for the great ideas!