I'm not sure what you mean by free - free from ratio requirements perhaps?
At any rate, the best porn trackers that I've come across all have ratio requirements - but all are fairly easy to maintain ratio too.
BlueLabel mentioned
pussytorrents, which is a great porn scene release site.
My personal favorite though is
Cheggit and signups are open right now:
http://cheggit.net/index.php. Cheggit has an implied policy of mandatory screenshots for every release (both scene and user-generated are there), which is - as any perv knows - critical; you want to know what exactly you'll be watching.

The search functionality, the content, the uploaders, and community in general make it a great - albeit less talked about - tracker.
Finally, another great tracker that isn't open at the moment b/c of database issues is
puretna. Be sure to check that one out in the next few weeks (months).
Hope that helps.
