You can Google for free proxies, but I couldn't get any of them to work. So I used this thing called Your Freedom. Once you register, you have access to their network of proxy servers. Then they have you download the Your Freedom program, which connects you to the optimal server.
Then you have your torrent program connect to the Your Freedom program. With µTorrent, I did:
Options > Preferences > Connection > the second frame Proxy Server
(make sure to have "use proxy server for peer-to-peer connections" UNchecked)
Connect Your Freedom and start up your torrents.
Note from Your Freedom website:
A rudimentary service is available for free. It will provide a bit more bandwidth than a modem connection and up to 3 hours of usage per day (1 hour continuously, up to 3 hours in any 24 hour interval, up to 9 hours in any week interval), and will probably be enough for all casual users -- it's certainly enough to visit blocked web pages and join chats, and if it suits your needs you are welcome to use it as much as you like.
For those who want more, upgrade packages are available. Please check out our Packages page for details. There are also upgrade vouchers available for those who don't want time based packages. Your bought packages and vouchers keep this service alive!