Here is an incentive card for your super spellers. Use a hole puncher to acknowledge their good work and reward them when they fill the whole card.
Something I found to work well was to have a gumball machine in the classroom. Instead of a treasure box or something similar, when the kids fill their punch cards, they can visit the gumball machine. Each color gumball is a different reward that the class came up with together (most free, in class incentives).
Hope you enjoy!