Use the following link to get a free $50 prepaid mastercard via Expedia:
Expedia July Sale: Book a qualified 3+ night hotel stay & get a $50 Prepaid MasterCard® card for gas! - Expires 7/31/09

Then enter coupon code: 09JUL10

I think this coupon code expires on July 10th.

If anyone manages to find some better coupon codes please post them. This is the best I could find.

Expedia seems to have the best rates, and they count towards the minimum hotel room requirements imposed by the hotel for the fine folks running Cluecon.

           
My total price after all the taxes and discounts for 3 nights ended up at $511.20
And that doesn't include the $50 prepaid mastercard.