I recently ordered a t-shirt from indiemerch.com. Everything went very smoothly and I'd highly recommend them. They offer a few different shipping methods, including USPS First-Class. I like this because it saved me a few dollars. A lot of websites don't offer that anymore. If they offer post office delivery it's usually just priority or priority flat rate box. After the order I received an email confirming my order.
Shipping was quick too. They emailed me a tracking number and my shirt was here a few days after my order.
I contacted them in regards to an out of stock shirt and their response was very prompt. Can't say enough good things and I can't wait for the other shirt to come back in stock.
The shirt was a nice weight shirt that feels like it will last. Screen printing quality seems very good. I'll see how it holds up after my first wash. Like the fit on the shirt. Some XL's are too tight on me and when I sit down the back rides up, this one is perfect.
There's a similar company in New Jersey called Loud Merch, which I've ordered from before. Their service was horrible and I wouldn't order from them again. They never emailed me about my order and it took them almost a week to ship. If you're backed up with orders and can't handle the business then obviously you need to hire more people.
Indie Merch for the win!