Starting at midnight UTC on June 8, 2011, a whole bunch of companies enabled AAAA records for their primary web sites. This corresponded to 5 PM PDT, 8 PM EDT, etc., and will continue until 23:59 UTC. A small list of sites that are usually dual-stacked (e.g., FreeBSD.org) as well as participating sites (Cisco, Juniper, Huawei) is available from RIPE NCC. There's also an IPv6-only site of the list which you can check out if you're dual stacked (or IPv6 only). If you would like to participate, but don't have a router that supports IPv6, ARIN has a list of CPEs that supports it out of the box, so you don't have to flash your device with third party firmware: D-Link and Netgear appear well represented; Cisco's Linksys, not so much.