This site is only reachable via IPv6. You are connecting from 3.15.15.204
My list of IPv6 only sites - add your own!
Top 100,000 IPv6 Websites - (Takes awhile to load)
Arstechnica - Everything you need to know about IPv6
Sixy - a list of dual-stacked/IPv6 only websites
Internet Society - World IPv6 Day
Hurricane Electric IPv6 Tunnel Broker
SixXS - IPv6 Deployment & Tunnel Broker
The only consumer class gateway/router under USD $200 I have found with good IPv6 support is the Apple Airport Extreme. Over USD $200 is the new Cisco RV220W.
[February 2012] There are more routers showing up with various levels of IPv6 support. Tunnel broker support (Hurricane Electric and SixXS) remains scattered.
[Feb 2012] Canon's latest printers apparently support dual-stack. I have not found anything about HP.
While you can find consumer level NAS devices that can be assigned an IPv6 address, other networking software needed to make everything seemless (mDNS for example) is not quite there. Samba appears to be working well in dual-stack.
Juniper Networks has an outstanding bug in their software that ignores IPv6. For companies that don't allow split-tunneling (while you are connected to the VPN, you can still use your local network, Internet-destination traffic goes through your local ISP, etc) the IPv6 route is left alone so you can effectively split tunnel between IPv4 and IPv6.
Google Webmaster Tools does not verify IPv6 sites. Lame.
[Update June 2011] Webmaster tools now verifies IPv6 only sites and grabs sitemaps.
[Update November 2011] Google now returns results for IPv6 only sites.
mDNSResponder only works over IPv6 on OS X. FreeBSD and Linux kernels are missing some parameters to allow IPv6 mDNS to function properly.
World IPv6 Day is June 6, 2012. Companies can turn on dual-stack sooner if they want.
[February 2012] Running tcpdump and noticed that IMAP and SMTP traffic to Google now runs over IPv6.
[February 2012] Google, Facebook and YouTube are both returning AAAA records for their www sites. Guess they didn't want to wait until June. Way to go! Apple however uses Akamai and apparently Akamai is not yet ready.
More soon...