Among the numerous DIY sites popping on the World Wide Web, I tried Custom Ink (www.customink.com). For promotional purposes, I tried uploading a graphic of a circuit board for a t-shirt design, but because it was really detailed, it was over 10mb. No worries, they sent me to another page, and I was able to get the file to them. Online or on the phone, the customer service was excellent. I was helped by Sarah Blair, who called me when there were some issues with the process. She explained the output of digital print versus screen-print, and assured me that if I didn't like the quality, I would be able to obtain a refund. You lose a lot of detail with the traditional screen-print, and a graphic designer would have to retrace some of the lines. She was good about calling me with print issues (e.g. ink colors and colored t-shirts). Specifically, on digital-preview, the graphic looked like it could be printed on a navy t-shirt, but she called to tell me it wasn't recommended.
To make a long story sort, details do show up. The photo was taken with my iPhone, sorry. You can choose from a variety of t-shirt brands (i.e. Hanes or American Apparel for that hipster). I'm really happy with the results.
Jonathan Cousins' cute little nerd is modeling and Orb shirt.