TeeFury.com does limited edition t-shirts that are only up for sale for 24 hours. They then print that run and send it out. TeeFury leans more on the pop culture side of these shirt sites and every now and then they have some great Lovecraftian shirts available. I own several Cthulhu and Lovecraft shirts sold through TeeFury.
Today they are doing a TwoFury where they pit two shirts against each other in a sale-off. Fortunately (or unfortunately for our wallets) they are offering two Cthulhu shirts.
Enjoy. I know I placed my order.