Good question, firemn; I've been thinking about the same thing for the cruise-chat cruise in August, '08. I know, it's a little early to start packing, but I like to plan ahead--it's half the fun.
I like to wear a suit and tie for formal night and blazer and open collar for other sea nights. On port nights, a nice resort or Hawaiian shirt over dress slacks.
On sea days, and excursions as well, shorts all the way and T's or light cotton sport shirts--I'm not much for polos; nothing against them, I just don't look good in them.
Dockers and polos just aren't my style and jeans, except denim shorts, are just not for me. I don't know what's good for the casino--I don't use it.
Well firemn, I don't know if this has been of any use to you, but it sure has helped me!
Have a great cruise.