I'm not the world's biggest fan of cupcakes. I can have one per year and be quite happy, but there is something compelling about a cupcake truck. If you are dying to get cupcakes in creative flavors at all hours and in various locations around Denver, look up Cake Crumbs. My suggestion would be to go to their website and sign-up for Twitter updates. That way you'll always know where they are and what the flavor of the day is.
FYI, this snap was taken at the Denver Public Library book sale, they parked the truck on Broadway and were doing brisk business. That's a snowball on the right and a lemon-something on the left. Delicious!