Xeeku

Xeeku Twitter is a full-fledged Twitter client which is fast and elegant with a streamlined GUI. It emphases simplicity and efficiency and gears towards everyday users not just techies!

Foursquare

Foursquare gives you and your friends new ways of exploring your city. It can be accessed via the web, iPhone, and Android devices.

http://foursquare.com/

Seesmic for Android

Seesmic for Android devices is a feature-rich Twitter application that’s simple and easy to use, but powerful and practical in helping you stay connected.

TwitterRide

TwitterRide is a Twitter client for the Android platform.

Logpost

Logpost is a free Twitter client for mobile phones. It works on Android, Windows Mobile, iPhone, Palm, and BlackBerry devices. It is primarily a web based interface which is customized for these phones.

Swift

Swift is a Twitter client for Android based mobile phones.

DroidIn

DroidIn is a client application for the popular social site LinkedIn. It is written for the Android platform and currently can be found/purchased on Android Market.

atweeter

atweeter a lightweight open source Twitter client for the Android platform.

twidroid

twidroid is a full-featured twitter & identi.ca app for android mobile phones.
Some of the features supported: