Though you didn't want another pizza truck, note that Pitruco (the other pizza truck besides Nomad) also does private events, and the menu includes breads and antipasti in addition to pizzas.
(Full disclosure: it's my truck; take my recommendations below with a grain of salt if you must!)
In addition to the two taco trucks mentioned above, Honest Tom's taco truck is also available for parties, though he may be tied up right now opening his sit-down place.
I'm betting you could also get the Smoke Truck (Mark Coates' awesome new BBQ truck) to do a private event.
You might also consider the Lucky Old Souls truck--excellent burgers, fries and milkshakes, everything made in house (down to the ketchup & mustard).
Finally, though they're not quite launched yet, the Strada Pasta truck will be available for private events--homemade lasagnas and pastas from a chef who trained in Italy.