My site's popular. How would YOU monetise it?
vulpes: I don't think you'd be able to get people to pay for premium features...what would they be anyways?  
I do have 1 idea:  
Sponsored tweet placement. Companies are probably willing to pay extra money for certain tweets to get special placement.Besides that you should get retweets/replies working, i wanted to RT a few things and got put off by the coming soon box.