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::8888http://code.google.com/intl/nl/speed/public-dns/docs/using.html
OpenDNS does have resolvers available too:
But these are as of january 4th 2012 not running the full service including malware filtering.http://www.opendns.com/ipv6/