I work right across Central from Food Truck Fridays, so we look forward to walking over there almost every week. My fave is Short Leash Dogs. I'm a vegetarian and happy to say that they do have a veggie dog that you can fix up however you like! Short Leash always has a long line but there are misters and shade so you won't die during the summer ;)
There are a lot of options so it's great if you go with a bunch of people - the only thing missing is a taco truck!!