According to Bink.nu, it’s going to be announced on February 16. My guess? Office 2007. Since some proposed names for Windows Vista were Windows Seven and Windows 07, and since the name of the current version of Office is Office 2003, I think a combination of the just-mentioned year and year format is a likely possibility.
I don’t think it’ll be Office 2006, since Microsoft already has an Office Small Business Management Edition 2006. (However, despite the version number, it just includes Office 2003 Small Business Edition plus Microsoft Small Business Accounting 2006.)
What are your guesses?