With the recent news that Utah will soon be joining the Pac-10 (up to 12, now), the league is widely expected to organize into divisions. Some in the Pacific Northwest don't like the obvious choice (Washington, Oregon, and Bay Area schools in one division, SoCal, Arizona, and Rocky Mountain schools in the other), as it limits regional exposure.
Another possible arrangement is this one; note that all of the traditional rivals are split apart (I assume that traditional rivalries will be maintained, and Utah/Colorado is considered a "traditional rivalry").
OSU, WSU, ASU, Cal, Utah, USC
Oregon, Washington, Arizona, Stanford, Colorado, UCLA
Other arrangements that come to mind?