Who could challenge Alabama?

As we continue to take a look at who should be No. 2 in the BCS standings, there's only one question that really matters in the grand scheme of things: Who can challenge Alabama?

So far, it hasn't looked like anyone other then the Crimson Tide can take down the nation's No. 1 team. Alabama has beaten people down with its power running game and held every offense it's faced in check with an extremely talented and disciplined defense. It's clear this is the nation's best college football team, but who out there can challenge the Tide?

Our ESPN.com colleagues took at look at four teams that have the potential to dethrone Alabama. Do any of these teams have what it takes to knock off Alabama in 2012? Is another one lurking?