It wasn't a secret that the Oakland Raiders brass were very interested in pursuing ex-49ers coach Jim Harbaugh this off-season. The Raiders were even prepared to make Harbaugh a contract offer on-par with the whopping six-year, $48 million dollar deal extended to him by the University of Michigan.

Has Michigan Gotten Their Man?

However, in the end, it looks like Harbaugh's old ties to Ann Arbor (he was a star quarterback there from 1983-86 under Bo Schembechler) was enough from the Maize & Blue to trump staying in the NFL with the Silver & Black.

In lieu of Harbaugh's decision to chase glory on the college ranks, here are some other candidates the Raiders might pursue for their head coaching vacancy.

Jack Del Rio
Del Rio has former head coaching experience with the Jacksonville Jaguars, and he's overseen the Broncos' vaunted defense since 2012. He's also a Bay Area native.

Brian Kelly
The Notre Dame coach is reportedly enduring a rocky relationship with school AD Jack Swarbrick. He's never coached on the NFL level, but is rumored to want to pursue that road before his career's over. Sports reporters for both Sirius XM and ESPN have linked him to the Raiders job this winter.

Brian Kelly on the Raiders' Radar?

Tony Sparano
Sparano took over for Dennis Allen as Oakland's interim head coach in Week 5 following the team's 0-4 start. The team seemed to respond to his style and enjoy playing for him, winning their last three home games of the season against respectable competition (KC, SF, and Buffalo). Rookie QB Derek Carr looked like he's developing into a strong cornerstone for the future under Sparano. He also has previous head coaching experience, having guided the Dolphins to the playoffs in 2008. Will that be enough for him to convince Raiders' management he's their guy?

Rex Ryan
Ryan was let go by the Jets on Monday after six up-and-down seasons with Gang Green. He's well-liked in many NFL circles. Many ascribe the Jets' poor 2014 to a lack of talent and a misuse of salary cap funds by GM John Idzik rather than a dereliction of coaching acumen in Ryan. Ryan's defensive capabilities are unparalleled and his brash, outspoken demeanor would fit right in with the Al Davis/John Madden Raiders of old.

Jon Gruden
"Chucky" oversaw the Raiders' last period of sustained success over a decade ago, and as long as he's in the MNF booth rather than on the sidelines with another team, his name will come up whenever there's an Oakland opening. However, he just inked a long extension to remain with ESPN. Sorry Raiders fans, but this one's a pipe dream.