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