Blizzard holds their costume contest every year at Blizzcon. In the last two years, a Mistress of Pain and Monk costume won. Unfortunately, this year there was no Diablo themed winner. However, there were many more Diablo entries as interest in this game rises. Here are images of the Diablo costumes. Click on any image for the larger version.
Blizzard also had their art contest with a Diablo entry winning 3rd place: