There was a lot of controversy in the Mac community when Apple announced they would begin using Intel processors in their newest machines. That's all said and done now, though, and it seems yet another door has opened. AMD is hinting that soon they will be providing Apple with processors as well:

This week, Ruiz delivered a key note at the Commonwealth Club in San Francisco, indicating that Apple would be using – not switching – AMD processors in the near future. "Knowing Apple, why would they want to be held hostage like everyone else has been? Everybody wants choice," said Ruiz.
Being held hostage is a harsh term, though keep in mind AMD has been taking to Intel to court for years over vendor locking. Interestingly enough, the article mentions that Apple has sold more Macs the year they switched to Intel CPUs over any previous year, meaning their switch to x86 may have been a long time in coming. It wouldn't surprise me in the slightest if they offered AMD-equipped Macs as well.