I found a page documenting the tile naming schemes of the various online map providers today. With that information, and the JxMapViewer component from swingx-ws, I was able to hack together a Yahoo Maps mash-up in under an hour.
The code still has a bug in it: latitude / longitude do not translate correctly. The marker on the map should be placed on London. I'll have to do some more tweaking to see if I can finish this up. The code needed to do this is surprisingly short:
