The official Twitter application for Android 2.1 just got released, and it looks good! It does make you wonder why there is no support for Android 1.6 however, as the majority of Android phones out there run on that version.
True to their open tradition, Google will be open sourcing the code used in the Twitter app very soon, and so Twitter and we are both very excited about the novel uses developers will create using Twitter APIs in their upcoming Android apps.
If you have a phone with Android 2.1, feel free to download the application at the Android Market.