First thing I would like to say is: Cafepress, take note. Contests don’t have to be just for US citizens. This Spreadshirt contest is open to anyone with a Spreadshirt.com account.
The design contest is called T-Summer Games 08 and they are for summer and sports related designs. Existing designs can also be submitted, you just have to add the tag “Sport08” to make them eligible. The competition runs from August 18th to August 25th and there are some pretty cool prizes including an 8GB ipod touch.
See Spreadshirt for more details.