I think McCain will end up going with Romney. Romney came out last week and said he'd love the job, and the two have made several joint appearances in the past month. I think Rice would be a better choice, but from where I sit I think the writing is on the wall. Romney will shore up McCain's lacking conservative credentials, just not as well as Rice IMHO.
As far as dems go...I think we will be looking at Obama/Edwards. Edwards officially endorsed Obama last week, meaning that his previously pledged delegates (115 or so) will now go Obama's way. Smells like a back room deal to me. Edwards is also safe...a well-known white Christian will help Obama shore up votes that he is losing to Hillary now (white working-class and less educated dems).
My $.02, but whichever way this all goes, I think its entertaining as hell this time around!