I came across Sphinx via the MySQL Performance Blog (which has some good entries you might want to check out). It is an Open Source Full Text SQL Search Engine.
The Riddle of the Sphinx
RTFM==QED
Sometimes you do something that surprises people. Jaws drop and wonder is seen in your friend’s eyes. You too can tap into these secrets of the ancients. See a source of hidden knowledge, known only to select few. Answer the riddle of the Sphinx, just by reading the manual.