Thinly slice asparagus and saute it quickly in olive oil (should still be crucnchy).
Thin sliced eggplant (Japanese-style eggplants -- long, thin ones -- make for a better presentation) also sauted until lightly browned in olive oil.
Roast your red, yellow, orange or green peppers first before slicing, then shake in a plastic bag with a little olive oil before using them as a topping -- yummy!
Add a little salt to all of these.
I live in Japan where you can find all sorts of "interesting" toppings on pizza -- canned corn anyone? But some of them work!
I also agree that sautéing the mushrooms (I like olive oil, but butter also is good!) before using them is the best way to avoid the dessicated mushroom taste and feeling.