Brinkster has a sweet free ASP/db combo, and MyCgiBin.com has a nice JSP/Servlet/db for free, but the only free sites I know of for PHP/MySql kind of suck.
Bear in mind my reviews are not based on recent experience, but I just visited a couple sites and it didn't look like anything had changed.
http://spaceports.com/ has your basic free site thing going on complete with obtrusive ads, but complicated and frustrating to set up PHP/MySql via email with 'tech' support, then the database is down half the time.
My rating: good for little or nothing.
http://coolfreehost.com/ was much more functional, although they disable mail(). I was on the adult side, so it might be better on the general public server, but the pop-ups were ATROCIOUS. Persistantly refreshing on close, and every page change spawned a new batch.
My rating: Nice place to develop, no place to invite visitors unless they offer less popups on the public server.
Adding... I did find one use for the second mention, they were a great place to test out the best free third party pop-up stopper software! THe winner: WebWasher