One way to promote your show is by wearing your logo, show name, tag line, on a shirt or hat. This video explains the pros and cons of using t-shirts. If you have the budget (and a rabid following) then purchasing t-shirts in bulk can be a strategy (realize its you who may be doing the trips to the post office). The alterntive is to do t-shirts on demand (but the price of the t-shirts are high). This video shows three on demand systems: Shirt City, Shirt Magic, and Cafe Press.
Since making this video, I have also played with Zazzle which has a nice interface. It resulted in a shirt that was also around $32.
Have you found a better deal? Let me know in the comments below