Adobe has made available the AIR runtime for Android. What his means is that you can now publish ActionScript 3 projects as native Android apps and submit them to app markets. Adobe claims that you can take an existing AIR desktop or a web app and transfer it to Android in a few minutes. You can use Flash Builder or CS5 to work with your apps.
The only problem is that currently it only runs on Android version 2.2,. which not all phones have upgraded to, and some phones can't run it.
To get started with AIR for Android you have to visit Adobe Labs and sign up to the pre-release program - the registration page isn't working a the time of writing but you can view some video demos and see some AIR applications running on an Android phone.
Introduction to Android 2 application development
Adobe AIR 1.5 Cookbook (Book review)
Adobe AIR in Action (Book review)
Teach Yourself Adobe AIR Programming in 24 Hours (Book review)