Since this is a hot topic, there have been many developments ...
As you might have seen on Fox yesterday, I believe conservatives ought to flat-out reject Tom Ridge. His selection would be a leap backward for the conservative movement (as it relates to the Republican Party), and should be treated as a "non-starter." I also floated the name of Utah gov. Jon Huntsman -- who is starting to generate a buzz.
Aside from Huckabee (whom I mentioned in the notes), one obvious name I left off the likely list was former Congressman and Ambassador Rob Portman. This was an obvious oversight, so let me add him to the list: Essentially, I see Portman in the same light I see Tim Pawlenty; He would not be an exciting pick, but he would also be acceptable to most conservatives.
If you're interested in this topic, Chris Connolly has some good thoughts on GOP "veep" picks, too.
Update: Another possible McCain pick? I think most conservatives would be excited about Rep. Eric Cantor.