Android: The Facebook app for Android has slowly been improving from its formerly awful state, but today it got the update many of you have been waiting for, adding a Chat interface as well as push notifications to the app.
Previously, Facebook chat was only available through apps like previously mentioned Trillian for Android, but the official solution works quite well. The chat interface is remarkably good on first look - you have your usual buddy list, with open chats at the top for quick access. The app will also send push notifications to your phone every time you receive a new chat, so even if you're not in the app at the time you can carry on a conversation. The app also includes some bugfixes and the addition of push notifications instead of notifications that require polling from the server. Notifications are still only available for event invites, friend requests, and messages, but it's still a nice touch.
Facebook for Android is a free download.