Elmer's Glue Stick and 3d printing, a set on Flickr.The Elmer's washable school glue stick (disappearing purple) increases adhesion between the 3d printing build platform and the object being printed. It is very easy to use and you can wash it off with water.
Updates and more information. (08/09/2013)
It looks like the Pritt glue sticks also works for everyone outside the US.
Pritt glue sticks link.
I did my two tests with ABS on a heated build platform.
Looks like the glue in the sticks are made with Polyvinylpyrrolidone (PVP),
I have been told that this trick also works with PLA and Nylon.
The rumor is that this is the same glue used in 3d systems Cube CubeStick.
Below is a video of Nylon being printed on glass covered with glue.