Tried the new Gourdough's doughnut trailer on South Lamar recently (http://www.gourdoughs.com/) and loved it. They sell over-the-top, loaded, fried-to-order doughnuts along with water, milk, and Dublin Dr Pepper.
I sampled the "Funky Monkey" (doughnut topped with maple frosting, a healthy amount of grilled bananas, and brown sugar/butter baste) and the "Mother Clucker" (doughnut topped with honey butter sauce and several fried chicken tenders). Both were good, made with huge crispy-on-the-outside-and-soft-on-the-inside freshly fried doughnuts, but I particularly liked the Funky Monkey.
Most of their doughnuts are $3.50. The ones with meat are $1 extra, I believe. You get a lot of doughnut for your money.