Although Hurricane Electric have free resolvers available for IPv6, these are often slow and returning results in seconds instead of milliseconds.
Google now has IPv6 DNS servers available too.
2001:4860:4860::8844 and 2001:4860:4860::8888
http://code.google.com/intl/nl/speed/public-dns/docs/using.htmlOpenDNS does have resolvers available too:
2620:0:ccc::2
2620:0:ccd::2
But these are as of january 4th 2012 not running the full service including malware filtering.
http://www.opendns.com/ipv6/