As someone who has bought a few t-shirts in the past from Cafe Press, can I give some advice to UK purchasers? They put the value of the item on the front of the package and any item over $18.99 or $19.99 (can't remember which) is liable for a customs surcharge. Therefore its better to buy singly rather than buying several at once otherwise you could find yourself, as I did, paying almost TWICE as much in additional postal & customs charges. So I suggest you still buy as many, but buy them SINGLY.
Have no idea if these are any better or not, but they might be worth a look:
http://www.99dogs.com/
Printmojo
http://www.99dogs.com/
Printmojo
Martin, just to be clear. I found Cafe Press incredibly efficient and I was WELL pleased with the t-shirts I got. It's just by buying 3 together I ended up with a price of $50+ on the front of the package and had to pay a HUGE (for me, I'm a Scot after all! 
) amuont of tax & cusoms duty that amounted to almost as much again. Therefore I suggest that anyone in the UK who buys a t-shirt (and I'll be one!) buys t-shirts SINGLY.
) amuont of tax & cusoms duty that amounted to almost as much again. Therefore I suggest that anyone in the UK who buys a t-shirt (and I'll be one!) buys t-shirts SINGLY.