You may have heard of the Tor network which if affectionately known as the onion router. Tor is a anonymity software which is free and open source. The trouble with Tor is that it can be dreadfully slow for every day use. Moxie Marlinspike has come up with a solution called Tor tunnel. Tor tunnel basically uses just the Tor exit node rather than all the hops in between. Of course this is not as good a solution for anonymity however in situations where you only need to be mildly anonymous it can be effective.
You can download the source for the tool here. You will need the BOOST C++ libs in order to compile tortunnel.
Once you have downloaded the source its the standard compile of configure,make & make install
Once you have it installed it, simply execute the tool with a IP address of a Tor exit node. If you do not know the IP address of a Tor exit node you can check here for some. You are going to want to look for entries with fast or exit next to them.
Once you launch tor tunnel, like this:
./torproxy 220.127.116.11 (Or whatever exit node you choose)
This will open a SOCKS interface on localhost:5060, which you can then point applications which support SOCKS proxies to. Be careful, though, remember that this is not useful for anything approaching strict anonymity requirements.