The question of finding good 3 column layouts comes up in the mail list from time to time. Here are some that I have found, along with a few notations about what features they include and how they work. The judgement of “good” is left to you and your needs. Each offers interesting techniques for the CSS student. By the way, when visiting these places, look around; many of these people offer other layouts that I have not included here.
Very nice to find all these, instead of partially re-inventing them, badly.