The best way to see what *all* your options are is to check the website of the International Association of Antarctic Tour Operators, www.iaato.org

Do not even consider going with any organization that is not a member of IAATO if you care at all about protecting and preserving the unique environment. (And if you don't care and just want bragging rights, I'd be happy to lecture you in a more appropriate forum.)

I went back in 1996 with a company that is no longer in existence, by the way. The advice I got at the time was to go on the smallest ship I could, which I think was useful given that gave me much more time on the ice itself.