First of all - I was somewhat surprised the Reds made Pete Mackanin the interim manager rather than Bucky Dent. However, I surmise from this that the promotion of bench coaches to replace fired managers is over in Cinci and that the search is on for a real manager.
That being the case (and I think it is), some possibilities:
Guys who managed in the majors last season who aren't doing so this year (so far) - Felipe Alou, Dusty Baker, Joe Girardi, Ken Macha, Frank Robinson, and Buck Showalter.
Macha is a part-time analyst on Red Sox broadcasts. Baker is working for ESPN as an analyst. Girardi is working as a Yankees broadcaster and also does regional Fox Saturday Baseball telecasts, and reportedly interviewed for the Orioles' managerial job last week. Robinson has said he doesn't want to manage again. I don't know what Alou's doing.
Guys from this year - Sam Perlozzo was fired in Baltimore. Mike Hargrove quit on the Mariners.
FWIW, Other guys besides those mentioned above who have managed in the majors from 2000-present who aren't managing in The Show as of now are listed below, and I did some digging - after all, I'm the CHFS - which is also included (Mackanin would have also been on this list but since he's now the interim manager of the Reds, he doesn't fit the criteria of “not managing in The Show as of now”):
Don Baylor - Forget it. Has been diagnosed with multiple myeloma.
John Boles - Mariners' front office
Bob Boone - Nationals' front office
Larry Bowa - Yankees coach
Bob Brenly - Cubs broadcaster
Larry Dierker - Astros broadcaster
Jim Fregosi - was a candidate to replace Bowa in Philly before they hired Charlie Manuel, not sure what he's up to now
Art Howe - Rangers' bench coach
Davey Johnson - working to earn Team USA a spot in the 2008 Summer Olympics and a consultant to Bowden in Washington
Tom Kelly - special assistant to GM for Twins
Joe Kerrigan - Yankees bullpen coach
Bruce Kimm - has managed in Cinci organization; no idea where he's gone since the Cubs fired him and hired Baker
Ray Knight - studio analyist on Nationals' broadcasts
Rene Lachemann - was coaching in Oakland last I knew
Gene Lamont - Tigers' 3B coach
Davey Lopes - Phillies 1B coach
Jerry Manuel - Mets' bench coach
Buck Martinez - Orioles broadcaster
Lee Mazzilli - Mets broadcaster
Lloyd McClendon - Tigers coach
Jack McKeon - sitting on his ass in Florida waiting for his phone to ring. I'm serious. Miami Herald said he went to a Marlins game, and that he wants to manage again.
Hal McRae - Cardinals' hitting coach,
Dave Miley - Yankees' minor league system.
John Mizerock - Managing Class A Wilmington Blue Rocks, the Royals' affiliate in the Carolina League
Tony Muser - Managing the Peoria Padres in the Arizona Rookie League
Johnny Oates - Forget it. Passed away on 12/24/04 in Richmond, VA.
Al Pedrique - special assistant to GM in Houston
Tony Pena - Yankees' 1B coach
Tony Perez - special assistant to Marlins' GM
Luis Pujols - Giants' 1B coach
Larry Rothschild - Cubs' pitching coach
Jerry Royster - Was managing Dodgers' AAA affiliate last year but got fired in September, not sure where he is now
Bob Schaefer - Oakland's bench coach
Joel Skinner - Indians' 3B coach
Jeff Torborg - Was a Braves broadcaster last year but wasn't retained for this year, dunno what he's doing now
Carlos Tosca - Marlins' bench coach
Alan Trammell - Cubs' bench coach
Bobby Valentine - Managing the Chiba Lotte Marines of the Pacific League in Japan
Gary Varsho - OF/baserunning coordinator for the Indians
Jimy Williams - Phillies' bench coach
Idle Speculation Department: Tony LaRussa's contract to manage the Cardinals is reportedly up after this season. And we all know that Castellini was formerly a part owner in St. Louis. Just sayin'.
Except for McKeon, I haven't offered any opinions here, “Just the facts, ma'am” as they used to say on Dragnet. FWIW, if I were Castellini, I'd have called McKeon already, but I'm not Castellini, so I haven't. As for my thoughts on the other guys listed in this post, I'll save 'em for downthread.