I stumbled across Re-Shirt last year, and while I have yet to post a shirt or purchase a shirt, I really dig what the site is all about. From the site:
Our idea is simple - to reuse old t-shirts and transform them into story-telling artifacts that become more valuable as they get older: Re-Shirts. We want to be a part of the solution for the global water crisis by raising the funds to solve it.
I have so many t-shirts that I have collected over the years that I don't wear, but can't quite bring myself to get rid of. I totally understand their sentimental value and love the idea of transforming them into something more than just a shirt (i.e. a "story-telling artifact).