I agree that there needs to be a way to discover API endpoints. Especially with the brave new world of SE 2.0 potentially leading to an ever increasing number of API-ified sites out there.
However, there isn't a good place to shove this functionality just yet.
Currently, we only have two places it could go:
- api.[stackoverflow|superuser|serverfault|meta.stackoverflow].com
- not "global," and accordingly shouldn't know about all the other sites in the network
- api.stackapps.com
- more "global," than the above, but also a site onto itself; it'd be a weird one-off to also have it serve up a network map
A similar problem exists with getting user associated accounts.
In short, once there is a place for this data to come from it'll be made available. Most likely, this will exist "out of band" from the regular API.
See StackAuth - /sites route - for endpoint discovery.