Tweetings is a slick looking client for the iPhone/iPod Touch. Former reports had it working for Windows but the new site reflects the mobile versions, all available through the AppStore for $0.99
They promote it as a clean interface with a ton of features:
It is focused on delivering a near feature complete Twitter API, such as seeing your friends/replies/messages, favourites, posting and replying. You can also search twitter, see trends, upload photos, update your location, find twitters near you and generate short links to post.
They have a great FAQ, Help and screenshot area of the website (which looks very polished). I hope they can send us one to test as we are being stingy 🙂