MetroTwit 1.0 released with multi-account support
MetroTwit is definitely one of the best Twitter clients I have used on the Windows platform.
The developers have just released the version 1.0 of the app. Prominent new feature is support for multiple accounts though it is a paid feature.
The changelog is pretty long compared to the last stable release. Check it out here.
If you want to get access to newer features faster, you can always check out MetroTwit Loop.