ActiveClans

Puddleopedia maintains a list of clans. Each clan has its own Puddleopedia page, which may include a link to the clan's own website.

Winds of Dawn has a Clan Directory, though it has not been regularly updated in a long time.

If you would like to know how active a clan is, you can look at Delta Tao's Clan Lord Informer, which lists characters who are currently clanning. The list can be sorted by clan.

iClan is a Mac OS X application that also provides the list of currently clanning characters. It allows you to highlight people of interest to you and can notify you when they log on.