One or more virtual or dedicated servers with root access, possibly located in the same data center. I'm running two Debian virtual machines (Lenny and Squeeze) but I assume you can adopt the recipe to work on any Linux box An account with tunnelbroker.net or similar service
All network configuration doesn't do any good if your web server software doesn't support IPv6 requests. For nginx this means compiling with the --with-ipv6 option. See my Human script for passenger w/ nginx for my favorite nginx compilation options.