Boid is a Twitter client heavily under development for Android with an interface matching the Ice Cream Sandwich UI guidelines.
There are tons of features missing currently but the app is looking solid. It got an update today which added a bunch of essential features.
However, a lot still needs to be done to make it a solid alternative to Twitter for Android and other apps.
The developers have already stated that they are aiming to creating an app that can match the quality of Tweetbot for iOS.
Tweetbot of course is one of the most popular third party Twitter clients for the Apple iOS platform. No version for Android is planned.