Redbubble is currently doing a 10% off sale for a week (ends June 22). On TOP of that, here's an online coupon for ANOTHER 10% off: ExtraSharp34505175 (input during checkout)
So really that's a 20% OFF SALE on t-shirts and hoodies!
ALSO, it's not on sale, but RedBubble now offers shirt designs to be printed as STICKERS. So check that out too! :)