The Wired How-to Wiki shows you 6 excellent bar tricks you can pull off for free drinks.  Make a bet with your friends and collect!  They’re not “obvious” tricks but from their descriptions, they all sound as if they would work easily.  It also shows you how to open a beer bottle with only a dollar bill (though any sheet of paper would work)!  That by itself makes this worth the read.  Any other tricks you may have up your sleeve?