Best "cross platform" app platform for Android?

Clients refuse to pay for "one native app per platform" in general (For smart business reasons many times).

While I think a pure native app on each platform yields a nice experience for the user, budget realities mean I must determine what non-native yet not web platform works well on many different types of mobile, especially Android (Blackberry, Winmo7 and Symbian are also nice to have) to give those prospective customers options.

It's not like the platform has to work without modification, they just need to work so MOST of the code is shared among the versions.

Any success stories you can point to on the web?

Any APIs with nice examples of complicated apps?

I'm especially interested in the playing of audio and video files local to the device as well as streamed.