Try TweetDeck. It's free and cross-platform. At the bottom of each column is a filter button where you can enter the name (or names) of people to filter out. You can also create columns that only include the tweets of certain people that you choose.

alt text http://content.screencast.com/users/NathanRidley/folders/Jing/media/a44ffec7-b33c-4e2c-954d-1465f1a27809/2010-07-13_1833.png

Try TweetDeck. It's free and cross-platform. At the bottom of each column is a filter button where you can enter the name (or names) of people to filter out. You can also create columns that only include the tweets of certain people that you choose.