SixXS

I don't know how valuable this is but SixXS does a little bit more than
provide IPv4-to-IPv6 tunnels. If you just want to visit a website on
the "other side" (without setting a tunnel up) just add
".ipv6.sixxs.org" to the hostname.

From IPv4

 
 http://www.ipv6.phreak.org.ipv4.sixxs.org

will take you to the
IPv6 site for the Digital Information Society. It also works in the
other direction. If all you have is IPv6 connectivity

   
http://www.google.com.ipv6.sixxs.org

will take you to Google.