I checked out a whole bunch of jquery tooltip plugins for a new website I just created, and just wanted to say that the best, IMHO, was Tipsy.

qTip and qTip2 is obviously very full-featured and beautiful, but overkill for my needs – the qTip 1.0.0-rc3 download weighed in at 38KB minified, and 83KB uncompressed. Holy smokes!! All that for a tooltip jquery lib?!

Tipsy is lightweight, and elegant, and the default css doesn't look half bad, unlike some of the other lightweight tooltip plugins I considered.