In no particular order:
Jeff Casteel, West Virginia DC. Casteel passed up the opportunity to follow Rodriguez to Ann Arbor last fall, but maybe a year of life under Bill Stewart—and the job security that goes along with that—might have changed his mind.
Many will be skeptical of the 3-3-5, but West Virginia finished 8th and 9th in scoring defense the past two years, though yardage was considerably worse (35th) this year. I also note that the recruiting class has an ton of safety/OLB types (Jones, Hawthorne, Gordon, Emilien, Bell, maybe the other Gordon) that are 4-5 spots on the field in the 3-3-5.
Corwin Brown, Notre Dame DC. Brown is a Michigan alum that Charlie Weis chose to be his defensive coordinator; before that he was an NFL DBs coach. In Brown's time at ND he's killed Chicago recruiting and racked up kind of eh results on the field. This year ND was 38th in total defense, 43rd in scoring. They were 65th in yardage in Brown's first season, but given the crater that was Notre Dame's offense it's hard to pass any judgments.
Brown's a high risk, high upside kind of guy. He'd be a dynamite recruiter if his returns from ND are any indication, but he's only been a DC for two years and hasn't exactly torn it up. More damningly, the defenses Notre Dame has run against Michigan the last two years haven't made any sense: ND sits back in a cover-two shell and lets running backs race up and down the field against them even with Ryan Mallett and Steven Threet the opposing quarterbacks. I guess it made sense this year once Notre Dame raced out to that lead. In 2007? Not so much.
Also, ND brought in TAH-NOO-TAH this offseason to be the "linebackers coach," but it seemed like co-coordinatorship at best. How in control of ND's D was he? Also also, he reportedly dissed Michigan when recruiting some kid, though he later denied he said such a thing.
Also also also: he has a giant umwellyouknow.
John Chavis, former Tennessee DC. Currently unemployed, Chavis was Tennessee's defensive coordinator since 1995. A pissed off Johnny Majors took a shot at Fulmer by praising Chavis:
“Frankly, I think (defensive coordinator) John Chavis has saved his job for 10 years.”
So there's that. In the twilight of the Fulmer era Tennessee was wildly variable on D: 4th in yardage last year, 70th in 2007, 50th in 2006.
Chavis is old and kind of looks like Gittleson so probably won't be a bang-up recruiter but the guy knows his way around a defense.
Paul Rhoads, former Auburn DC. For fans of irony this is choice A1, as Rhoads was Pittsburgh's defensive coordinator in 2007 when the Panthers held a mostly Pat-White-less West Virginia team to nine points and precipitated the string of events that ended with Rodriguez taking the Michigan job.
Auburn's defense was 27th in yardage and 15th in scoring this year despite taking the field opposite and offense that was the functional equivalent of Michigan's. That chaos butterfly of a Pitt defense was fifth in yardage and (somehow) 42nd in scoring. Wikipedia on Rhoads' Panther career:
In 2000, Rhoads was hired as the defensive coordinator for the Pittsburgh Panthers by Walt Harris. In his first season, Rhoads was credited with improving the team's defense to their best performance since 1980. In 2001, his defensive unit ranked among the nation's top 30 in five different categories at season's end. Additionally, Pitt finished with 38 quarterback sacks. In 2002, the Panthers defense ranked among the nation's top 25 in an impressive seven different categories. In 2004, Pitt ranked ninth nationally with 17 interceptions and Rhoads was kept on staff by new head coach Dave Wannstedt. That decision proved wise as by then end of the 2005 season, Pitt was ranked second nationally in pass defense (yielding just 152.82 yards per game) and sixth in pass efficiency defense with a 99.36 rating. In 2006, Sporting News named Rhoads the Big East's best defensive coordinator. In 2007, Rhoads' defense was among the nation's leaders in various categories, finishing fifth nationally in total defense (allowing just 297.7 yards per games) and third nationally in pass defense (allowing just 167.3 yards per game). While the team finished 5–7, they ended on a high note by holding then-#2 ranked rival West Virginia to a season-low nine points in a 13-9 victory in the Backyard Brawl, limiting the Mountaineers high-powered offense to 183 yards (292 yards below their average).
Even setting aside the irony, Rhoads appears to be a good choice. He has eight years of DC experience, most of which is impressive. He's a guy Rodriguez has gone up against a half-dozen times, so there's some familiarity between the two coaches. He's young enough (41) to be an energetic, motivated recruiter. A guy like Tommy Tuberville surveyed the nation after losing Will Muschamp and picked him out, and Tuberville can find himself some defensive coordinators.
Hell… what about Tommy Tuberville, former Auburn head coach? Tuberville may want to sit on the sidelines for a while or whatever, but the parade of defensive coordinators that worked their way through Auburn never seemed to have much impact on the fortunes of the D. Tuberville was a DC for one year at Texas A&M before getting the Ole Miss job.
Eh, this one's pretty far-fetched.
Vance Bedford, Florida DBs coach. You know Vance from his two stints as Michigan's DB coach; those sandwiched an up-and-down career as Oklahoma State's defensive coordinator. This year he's vastly improved a previously porous Florida secondary.
But… no. Bedford's last stint as a DC ended in ignominy and controversy after he called Okie State fans "roaches" and then wouldn't back away from it. We all know how that sort of comment would play in this media environment. Also he wasn't a good DC; as long as Rhoads and Chavis are out there there's no reason to go back to a guy who didn't do well in a coordinator role before.
The Orgeron. Come on. You know you want him.
Chris Spielman. I'm kidding. Okay, I'm half-kidding.
So, who do I like?
Of the listed: Rhoads. He's got a good track record and could revive Michigan's Pittsburgh-area recruiting. After that, probably Corwin Brown, actually, for recruiting/piss off ND/Michigan alum issues.