djangopeople.net, GeoDjango and PostGIS
I don't know what it is about geographical data, but applications that use it are seriously cool.
Mentioned on Michael Trier's "This Week In Django" podcast, (also available - free - through the iTunes store), djangopeople.net is a great way to find out who's doing Django stuff near you.
Thankfully, it's not trying to be yet another social networking site. It's simply a Google Maps mashup letting you view basic details about people, what they do, and where they're based.
So I want to know where you are - if I'm doing Django work, and I need extra manpower, well, it sure helps if I can see you're nearby!
PostGIS and GeoDjango
Also mentioned on Michael's podcast are the GeoDjango branch and the PostGIS project that it's based on. PostGIS puts a number of spatial datatypes into PostgreSQL, and GeoDjango builds onto that. Given the current explosion in mobile technology, I would venture that this branch of Django is going to be the basis of some exciting, spatially-aware applications in the future.
I'm definitely going to be checking this branch out, and perhaps even downloading the iPhone SDK when it arrives. With Jobs' announcement of iPhone/iPod Touch support for Wi-Fi locations, everything's starting to come together nicely. Exciting times!