I think CXP, Platinum Coins, and an Exclusive Weapon/Item is an excellent suggestion and would make for a better, more personally valuable set of prizes than a Gift Card; not that there is anything wrong with a Gift Card. I think all combatants should receive a gift card as incentive to and an appreciation for their participation as a consolation prize if you will (It would also drive more traffic to their store)
And in addition to the aforementioned prizes, a unique victory title.