The best milkshake I've had in years was from Full Tilt using their Thai Ice Tea ice cream.
I was going to say Full Tilt also cus I make milkshakes myself there. Right now at the UD location you can choose between Cardamom, Mint Oreo, Milk Chocolate, Chocolate Chewy Core (w/ cookies made of cranberries, honey, coconut and nuts), Chocolate covered Cheetos flavor, Bourbon Maple Walnut, Lemon Chocolate, Chocolate Mint Oreo, Salted Caramel (BEST for shakes. Well, that or Horchata or Coffee Oreo, or Cookies 'n' Cream), Vanilla Bean, Lemon Marshmallow, Toasted Coconut(Vegan), Pina Colada(Vegan), and Peach Strawberry Sorbet(Vegan). We use coconut milk for the Vegan shakes and they're totally delicious.