This is kinda spoilery regarding the next episode

Spoiler Alert, click show to read: 
According top the previews I saw, in the next episode, D'anna gets unboxed by Cavil and Boomer, but she immedietely breaks Cavil's neck and manages to join up with the rebels.

Once she does, she meets with Roslin and the others and reveals that one of them is the final five. Now, in the previews it shows Roslin shocked right after 3 said that, but it might not necessarily mean her. The problem is, we know that Tigh, the assistant person, and Tyrol are on Galactica. That only leaves Anders who we still don't know yet is on the baseship. That means that we may be able to find out who is the final fifth cylon of the final five