Tomatoes are also one of my favorites to smoke. One thing I have found, though, is that smoking your own sausage and then putting it with your favorite jarred pasta sauce and simmering for a while will impart the smoke flavor to the tomato sauce. Even bites with no sausage have much of the intensity of smoking the tomatoes directly. If you freeze a few links of sausage, it's an easy way to have "smoked" tomato sauce on a busy night!
I love smoked "baked potatoes." Clean it, put a bit of oil on the grate, and smoke it -- I think a couple of hours (don't have my notes now). To 195 degrees internal, I think. I find I don't need to add butter or any other fat. Just salt it and eat it.
Smoked plums are another favorite, and they are currently in season. Intense plum flavor that goes well with creamy vanilla ice cream.
Smoked garlic is very good, as noted above. Very soon I want to try to use smoke garlic to make aioli.
I know you said "other than meat," but my absolute favorite thing to make in my smoker is chipotle smoked-tuna salad. I get fresh tuna in 1/2 lb chunks (I have a fantastic fish-monger), lightly oil the grate, and smoke it about 1 to 1.5 hours to 140 degrees internal. Smoked this way, I find the tuna itself to be disgusting, and I love smoked fish. But take a potato masher to break it up, and combine it with a lot of adobo sauce from canned chipotles, mayonnaise, sweet pickled peppers, yellow mustard, and salt. Also add pureed chipotle peppers to taste (I use 2-3 for 1 lb of tuna). You can also leave off the adobo and chipotles, which I do for my daughter. Everybody raves over it, including my daughter who insists on taking a milder version to preschool for lunch.
I've tried lots of stuff on the smoker that didn't work. Smoked brussels sprouts was one of my worst. Could be that I did it wrong!
I can't count the number of things I "grill smoke." Mushrooms, asparagus, green beans, parboiled whole fingerling potatoes (with aioli), grapes, pineapple, apricots, on and on.