Tweetie

Tweetie is a Twitter client for Mac that has a few different interesting features, such as the ability to review the full history of a conversation and a search feature for trending topics.

The message composition window in Tweetie is independent. This means you can write a quick tweet and then send it with a simple shortcut (Command + Enter). You also have the option to shorten URLs. From the preferences panel, you can link various Twitter accounts so you can use them from this application.

Tweetie also lets you check mentions and private conversations, as well as access your favorites, followers, and those you follow.