Convenient public IPv6 test addresses

Solution 1:

The shortest I've seen is www.sprint.net (2600::).

Solution 2:

Handily enough, 2001:4860:4860::8888 and 2001:4860:4860::8844 are the IPv6 equivalents of 8.8.8.8 and 8.8.4.4!

That's fairly easy to remember.