If Jon Paul Morosi is to be believed, then it looks like the candidates have been narrowed down to Mel Stottlemyre and Roger McDowell.
I've talked about Stottlemyre before. McDowell was the pitching coach at AAA Las Vegas in the Dodgers organization last year, where the only guy to turn in a respetable performance was someone named Franquelis Osoria. Las Vegas is a hitter-friendly environment, and a pretty extreme one at that (on par with Ameriquest Field), but the team ERA was 28% worse than the league average, and its K/BB was 17% worse. The brightest prospect on the team, Edwin Jackson, regressed from what was already a pretty awful 2004 season with a total nightmare of a 2005 campaign.
Here's the real scary part, though - by taking each pitcher's K/BB ratio at his previous stop and weighing it for the amount of innings he pitched in Las Vegas, you find that the staff as a whole underachieved by 39% (in terms of strikeouts to walks) under McDowell. Some of this is due to many pitchers facing a higher level of competition, along with the general across-the-board deleterious effects of pitching in a bandbox, but still, that's hardly an encouraging bit of support for McDowell's case.
It probably doesn't mean very much, since analyzing the effect of pitching coaches is hazy at the best of times, but when it's all you have to go on...well, it's worth thinking about.