http://www.gridstream.org/ a fan run ingame radio station. (legal and free)
Music, big ingame parties, guests (Ingame support, Funcom, Players), contests (can win both ingame "credits" and sometimes real world prizes given by Funcom (makers of Anarchy Online).
GridStream has been broadcasting since spring 2002, and is one of the oldest (still alive that I know of) and biggest MMO radio stations.
(yeah yeah, I know. nasty self plug there. I'm Gridfan of Gridstream Productions)
I'm not aware of any other "free" MMO's. At least not commercial "grade" ones.
One could only hope that the likes of Eve, Star Wars Galaxies, Matrix etc follow suit and provide the basic account free.
As it's a perfect way to introduce people, and gets rid of the annoying 14day or so trials most run that never give ya enough time to test things out.
At least with AO's solution you get a year+ trial if you will.
Costs are covered thru ingame billboards spread around cities and so on,
many of these billboards existed previously as well, and had story and similary related content.
They aren't really intrusive at all, and actualy fit into the environment.
As a paying customer, the ads are disabled, but myself I decided to turn them on again as I find them entertaining or brings a bit more "life" to the cities as well
