Sat Twitter - enables users of satellite devices to update their positions
Mailana - Twitter social network analysis that graphs you amongst the tweeps you most often have contact with. It ignores direct messages and ignores transactions where you were sent a reply but you never replied back as it makes an assumption that you don’t know them.
It lists who you should follow, friends in your location you have talked to before, friends in your location who have talked to other people in your location, local people you follow, local people who follow you, who of my friends talk about a certain topic.
Also see Tweet Wheel.
Hey, I posted about this already, Top Twitter Friends.
Favrd - a stream of highly favourited tweets. Not sure if this is a total popularity measure, as I use the favourite function for stuff to read later.
Tweeter tags - yet another directory, but this one is more like an expert locator.