I've started taking the bus to work, and I like it except for one thing: they're never on time. I really hate waiting around for the bus! I saw that King County has a Bus Tracker, but it is a Java Applet. I really hate Java applets, so I decided to write my own. I found that UW provides a WSDL interface so I can get live bus information. I've put up a preliminary release, and I'll get a domain name for it and build it out more soon.
Anyway, you can click here to see my take on the Bus Tracker.
I don’t know if it meets your needs (maybe you just wanted to play more with Ruby), but there’s a great Google Maps/Metro Bus Tracker mashup:
http://www.busmonster.com
Why do I have to find out about these things after I write my own? That is very annoying. This thing looks cool, but the maps don’t seem to show up. Maybe its a bug?