Tommy's dates from back in the early 1970s, when Coventry was a proper hippie enclave. Today, they're still known for their milkshakes and extensive vegetarian offerings, but the menu has been expanded to have more or less something for everyone, carnivores included.
As everyone else has said, the milkshakes are the real stand-out here. There are a ton of different options, all customisable, and I've yet to try one that I didn't like. The food choices are extensive: you'll be presented with a selection that looks more like an encyclopaedia than a menu. I'm a big fan of the Donovan and Wildflower falalfels, and the black bean chili is also a must-try. Everything is very reasonably priced; there's basically nothing on the menu that's more than $10.
Service can sometimes be spotty, and there can be a long wait for a table at busy times (no reservations), but the good food and cheap prices makes this somewhat easier to bear.