Threadless presents the "Wear I $pent my summer vacation" sale! (Tshirts for US$10)
They have just emailed me to tell me about thier sale, where they have various items on the site from $10 (US) and upwards through to June 3rd. They have some amazing designs, and every day they will be announcing a new one. With the US exchange rate at the minute, these are very good prices :)
If you want unique tees, this is the place to look!