Holyshirt.com, I have several custom/special event shirts from them. They hold up well and aren't to bad for prices assuming you can meet a minimum of pieces
That's one big thing you have to look out for. I've had screen-printed shirts ranging the whole spectrum; some only lasted 2-3 washes, others I've had for many years and they still show no sign of fading/cracking/wear on the design. Make sure the company you use stands behind their work, and guarantees the screen-printing will last.