Restaurant.com provides discounts when you eat out. For example, you can buy a $25 certificate for $10 and then when you eat out at that restaurant for $50 worth of food, you only pay $25. Thus the total you paid comes to $35, instead of $50.
But the trick is to wait for their promotions when you can get that $25 dollar certificate for $1 or $2 too. Then the total you pay for that $50 food would be only $26.
Another trick is to do your credit card bonus spending for new credit cards at restaurant.com. Then you get double discount, one to eat out via restaurant.com certificates, and another for the new credit card bonus.
You may sign up Restaurant.com here.