The problem with Buyyourfriendadrink.com is that you have to use one of their participating bars. GiveReal.com solves that problem by allowing you to use a credit card you already have. Let me 'splain.
Let's say you want to buy your friend a round for helping you move that Bowflex in to the laundry room where it can serve some actual use. You can go to GiveReal.com and put some money in to their account. Your friend gets an e-mail stating that you bought them a drink which then allows them to go on their site and register their credit card. They can then use that credit card to purchase their drink at ANY restaurant or bar in America.
Since we've all become Facebook junkies, they even have a Facebook application. Finally! An application that you might actually use that doesn't involve a sex test or throwing a snowball at someone!