Most people when they think barbecue, they think hamburgers, steaks, ribs, and all that other nasty stuff. Then once you vegan, you think prepackaged frozen veggie burgers, corn, maybe some tofu steaks. It's pretty sad. But there are plenty of great ways to have a vegan barbecue without a ton of over processed foods. Just think, veggie kabobs, (zucchini, yellow squash, peppers, onions, whole mushrooms, etc) add in some tofu, seitan or tempeh on there if you're feeling fancy. Grilled plain old vegetables. Such as corn, peppers (I prefer red) zucchini (makes those perfect little grill marks you see in magazines) onions (I've heard you can do them whole, but I usually grill them in thick slices) whole mushrooms, whatever.
Homemade burgers, like black bean. (I made the ones from Veganomicon, precooked them a little in a pan first, then grilled them and they came out great. Be sure to baste them with a little sauce of some sort though, because they will dry out a little) Another thing that works as a great burger is the portobello mushroom (I've never been quite sure how you spell it though...) It comes out magnificent as is with a little olive oil and balsamic vinegar.
There's also the homemade or store bought hotdogs/sausages, but I'm not too into them.
And there you've got a great barbecue. Burgers, kebabs, corn, grilled vegetables, maybe some coleslaw or a salad, or potato salad to go with it. Yummy. I'd go to that barbecue any day.
Another Google image...