CB and a few others have found some evidence of the official Twitter client from RIM. We haven’t seen anything in terms of screenshot leaks or details, but hopefully RIM is working on something unique, as there are already a plethora of Twitter clients available. Generally speaking, when RIM is developing an application, it’s because the app will have access to more APIs than a third party developer would normally have access to. This is why they built the Facebook app.
We’re not positive about a release date, but rumor has it the client is in testing and we should expect something before February.