The rider list is the only missing feature that I had expected to find.

Seems that there are two areas to cover: who's on Twitter and what are they saying. As for who, definitely add more information but consider grouping the riders for context (by nationality, team, specialty, recent/upcoming races, etc.). Consider adding a text box to suggest another rider.

And as for what they're saying, a sort of "mute" button would be nice; Burke Swindlehurst is funny but a little too prolific. Perhaps allow the posts to be grouped by rider. That way Dave Z fans won't miss his infrequent posts, such as "Raced through a town called Bonar today..."

Ok, I added the complete list. I think working on some categorization/user ratings sounds good too. Thanks!