BitBlinder helps torrent downloaders stay anonymous, avoid filters
The installer includes the BitBlinder client, relay server, SOCKS client, and Portable Firefox (with the TorButton add-on installed). The client itself is a modified version of BitTornado and anonymity muscle is provided by TOR. While it lacks some of the options of other torrent clients, key customizations are available in the preferences pane -- limiting upload / download speeds and maximum connections, for example.
BitBlinder offers four levels of anonymity - off, minimal, normal (the application default), and the TOR standard. Increasing speed means, of course, that you're sacrificing some anonymity -- and you'll be notified as you move the slider around.
Now, on to the 'free' part of the promise. When you install BitBlinder, you get credits for 3GB worth of transfers. To earn more, you'll need to set your machine up as a relay server. BitBlinder won't work without community participation: if there's no one online to help proxify torrent traffic. The relay app does allow you to specify limits if you have bandwidth cap concerns.
If filtering and privacy are big concerns for you, go and sign up for the BitBlinder beta program. It's a hassle-free way to wrap your torrent downloads a shroud of anonymity.