Albert Einstein (1879-1955) directed the Phisics Institute from 1914 to 1933, when he had to go away.
Marlene Dietrich (1901-1992) started in Berlin her career, and is buried at the Friedenau Cemetery.
Grimm Bros. (1785/6-1859/63) famous for their fairy tales.
Hegel (1770-1831) gave classes at the Berlin University from 1818 till 1831
Bertolt Brecht (1898-1956) has got a Museum here, where he lived.
Klaus Wowereit is the mayor of Berlin. As far as I know he was the first "officially gay" mayor of Germany - and he definitely fits perfectly to Berlin because he is cool! (Well, I don't know many mayors with a fancy Flash Website that is available also in Turkish! ;)
He came out as gay with the sentence 'Ich bin schwul - und das ist auch gut so' (I am gay and that is good so) before he was elected and it became a rather popular statement.