Besides, web/dns/mail, perhaps user configurable tests - service:port
ie: I also have an IPv6 capable icecast server.
I amke sure IPv6 capable is very important!
I also have anoncvs, cvsync, rsync, and SILC on my server.
...And I have NNTP. Although an older service, Usenet is a major service.
what's about a Jabba server ?
or at least to be able to communicate via Jabba over IPv6? this could be something for the NewB or Explorer level.
providing a "The Onion Router" (TOR) could also be a service from which the community would profit.
What about NTP?