One of my favourite sites for tshirts is designbyhumans.com - which works on a similar basis to threadless, ie the designs are mostly user submissions which are then voted on by other users. The result is a tshirt of the day, which can become tshirt of the week and tshirt of the month. At each stage the designer gets wads of cash (I think I’ll do a separate post about the amount of money designers can earn on these sites.
Anyway, one of the advantages I feel DBH has is that it uses multiple printing mediums, such as using gold leaf and texture for this fantastic tee:
And their prices are reasonable - slightly higher than Threadless at $19 versus $15, but great value.