NASA Federal Credit Union has a credit card offering a tiered cash-back plan:

Earn 1% of each dollar of new net purchases from $0 to $1,000; earn 1.25% of each dollar of new net purchases from $1,001 to $2,000; earn 2% of each dollar of new net purchases from $2,001 and above. There is no limit to how much cash back you can earn. The rebate credit amount will appear on your monthly statement and will be applied to your account annually in your November Statement.

You must be a member of the credit union to apply for the card, but membership is relatively easy to come by. You are automatically eligible for membership as a NASA employee or an employee of one of many selected businesses. Otherwise, you can be approved by joining the National Space Society for $18.

Link (via FW)