Uniqlo.com has great t-shirts with cool themes from amazing artists and they last for years. The only downside side is they get sold out as soon as they are released and you have to wait for the next batch to come in..
I have had good results on several recent orders using CustomInk.
You may also want to look locally. I came across a place that is local to me whose prices are competitive with CustomInk and it's nice to support the local business. Also no shipping. I'm sure they also do remote orders, so you can check them out too: http://eastcoastembroidery.com/