Sean Bean, played Boromir in LOTR. Also played Sharpe in Sharpe - in fact, that role is somewhat similar to Geralt (badass who gets all the girls), so I think he'd fit perfectly.
EDIT: To clarify, I'm answering Magerette's question.
By God it is Sean Bean! I knew he looked familiar but the white hair threw me. I agree he was perfect in the Sharpe series--one of the few tv series that lived up to the books it came from (by Bernard Cornwell.) He would be an excellent Geralt. Thanks VPeric.
What about all the young lovelies? How about Keira Knightley for Shani?