Using SL4A (which has already been mentioned by itself in other answers) you can run a full-blown web2py instance (other python web frameworks are likely candidates as well). SL4A doesn't allow you to do native UI components (buttons, scroll bars, and the like), but it does support WebViews. A WebView is basically nothing more than a striped down web browser pointed at a fixed address. I believe the native Gmail app uses a WebView instead of going the regular widget route.
This route would have some interesting features:
- In the case of most python web frameworks, you could actually develop and test without using an android device or android emulator.
- Whatever Python code you end up writing for the phone could also be put on a public webserver with very little (if any) modification.
- You could take advantage of all of the crazy web stuff out there: query, HTML5, CSS3, etc.
