I've never ordered from them, but a lot of my friends have had good experiences with
Prographics Sportswear . They also go by
greektshirtsthatrock.com. Their prices are really good, and for girls they have a HUGE selection of cute imitation Lilly Pulitzer and Vera Wang fabrics for sewn-on letters. The only odd experience I had was a few months back, I requested a quote for some shirts from a few companies and ended up going with another one because they got back to me first and we were REALLY tight on time (as in, the event was in two weeks days and someone dropped their procrastination in my lap

). Prographics called me a few days later with their quote and I politely told them the situation and that we were all set. The next time I requested a quote from them they never responded. I don't know if it was because of the first experience or if it was just a mistake... I never followed up to find out. I guess I can't really blame them not to trust me!
The company I DID use for that order was
Greek101, and they were great... I went from price quote to shirts in-hand in about a week and a half (and I didn't pay any rush fees!). They also gave us a great discount for using their logo on the back of the shirt, but don't count on that... they had worked with another group on our campus already, plus we were ordering 200+ shirts for an all-Greek competition, so it was kind of a special circumstance. I don't know if they'd do it for just anyone. Anyway, I'd recommend them - especially if you're in a rush!
Metro Greek has absolutely adorable designs for both fraternities and sororities! They'll also do custom art for you that looks really sharp. We're ordering most of our recruitment shirts through them. The artwork is great and they're really good about revisions. The work is good quality. They tend to be a little pricey, but its only because there are a LOT of colors in the designs. I would highly recommend them.
I used
Rainmaker Graphics recently for an order and was really pleased with them. They sent me a huge box of freebies and catalogs a few months back, then followed up to see if anything piqued my interest. The contact person I had was VERY prompt (he would email me back within an hour if I had a question) and professional. He also put up with about 5 revisions I wanted done on the art design they came up with, and they didn't cost anything. The prices were very good and the products were good quality. The only complaint I had was that they messed up my shipping address and I had to pay to have them shipped to me, but they were very apologetic and offered to pay me back for the shipping costs and give me a discount on my next order. If I had needed the shirts in a rush it would have been an issue, but I think it was probably a one-time thing. I would definitely recommend them to other Greek groups.
I've used
Custom Ink a few times and they're very prompt, with great customer service and a really cool DIY online design tool. The t-shirts were good quality, but be aware that they don't always look the same as they do on the design tool. My only real complaint is that they're very pricey compared with other companies! A lot of Greek groups I know design their shirts on Custom Ink, then send the proof to a cheaper company to have the shirts done
Hope that helps!