This is the original RepRap test object...

http://reprap.org/wiki/File:Minimug.stl

...a small shot glass which should be water (ahem) tight when printed on a properly set-up machine.

It has been uploaded to Thingiverse before:

http://www.thingiverse.com/thing:36

For whatever reasons, however, both here and on the original RepRap wiki, the minimug model has been presented rotated on its side, in an unprintable position. A rite of passage, perhaps? So that first-timers are obliged to figure out how to rotate the model before they can print it? If so, sorry to break with tradition, but it seems decidedly beginner-unfriendly.

This is the exact same model, but it has been rotated into an upright position, centered at the origin along X and Y axes, and positioned with its lower extremity exactly on the origin along the Z-axis.