ping, traceroute, tracepath, 6bone registry, DNS: JOIN / Testtools (German language only, but should be no problem for non German speakers)

traceroute6, whois: IPng.nl

AAAA Lookup Checker http://www.cnri.dit.ie/cgi-bin/check_aaaa.pl

List of worldwide all IPv6-aggregated IP-Blocks

DRENv6 Looking Glass

IPv6 Prefix Calculator by TDOI

DNS record checker