I've been messing around a bit with ip information, proxy detection, and geolocation at work, and wanted to build some of my own services in order to get a better understanding of them. So far, the only thing up at http://ip.emmesdee.com is a basic replacement for ipchicken and whatismyip, but what's been slowing my experimentation has been a couple of surprising limitations in Google App Engine.
In order to check for a tor proxy via tordnsel, it would be much easier if GAE could perform DNS queries. You have to think this is coming with their recent announcement of public DNS servers. (I wish they would host DNS too! dotster charges $10/yr for dns, and my friends down under have had problems with godaddy DNS)
In order to do basic geolocation, it would be simplest if I could just import a sql database and query it. Unfortunately, it is still far easier to just bang out a little PHP than it is to figure out how to migrate to BigTable.
All things considered, GAE still feels a bit beta, but hopefully these problems will be gone in another year or so of GAE.