StickerMule make really great stickers as anybody who took advantage of the previous deal would probably know. They also make custom magnets, buttons, labels, coasters, wall graphics and packaging.
They have introduced a referral system where both referrer and referee receive AU$13.70 store credit. The credit will be given once the referee has made a purchase.
After you sign up (via the random referral link below) you can add your own referral link to OzBargain's referral system here. I would encourage you to only sign up if you will make a purchase from their store otherwise neither you or the referrer will receive credit.