I agree with yousirname, about Frakes. My buddy pointed out how he's so wooden and stiff and always cocks his head and walks crooked. Now I can't ever see him NOT looking that way.
I remember being absolutely shocked when I saw Sirtis name in the credits of Granda's The Return of Sherlock Holmes episode The Six Napoleans (the series where Jeremy Brett was Holmes). She played Lucrezia, the Mafia Boss' daughter that was dating Beppo, the man that was breaking the statues. I was shocked not only at the difference in her looks but also her acting abilities (even though her part was small in that episode).