Thank you all for your suggestions. I discovered one myself by accident today. I got a last minute request from DH to book 2 night at the Marriott Tysons for his friend arriving tonight. I check the price on Marriott.com and was shocked to find it was only $89 per night with the $100 voucher offer. Then I thought I might want to get them the rate with breakfast for Friday night. As soon as I changed to one night, the rate went up to $269 for tonight. I know weekend rates are lower. But I never knew it could pay to book two nights sometimes. So not only the rates for two nights total are $100 lower than one night, they also qualified for the $100 voucher.