Custom Shirts - Where?

Over the years, I've been getting requests from some people about having a few of the designs that I've made available as shirts.  I always thought it was "one of those things" where it could be much more effort than it was worth.  However, as selfishly as this might be, I've just made a few personal designs that I'd like to have made as shirts.  As such, I could make a few of the designs available including some new ones.

However, I could use some guidance in choosing a service.  I figured that the art community (and hopefully a few of the people who will stumble upon this entry) will have a better idea than me (which is none!)  One with some sort of storefront would be nice.  Any ideas?

Thanks in advance!