Personally I loved my WIMM One ($199) developer watch, which was more powerful than any of the others, because it included WiFi, so it could update its news readers, weather, etc without needing a phone mothership for comms.
I had no problem creating my own test app for it, and it included a watchface SDK.
Unfortunately, (WIMM Labs) was bought up by someone unknown.
Whoa. Google just confirmed that they're the ones who bought WIMM Labs last year.
Very interesting. Google must have a watch project going, as well as Glass.