Running two amps into one cab is one option. Another I used to do is run a mono rack rig, but run each side of the power amp into the two separate speakers. I'd mic one and set it's level for the soundman, and I'd set the other for the stage volume I wanted: essentially I made my own stage monitor for my guitar amp.
Those old Mesa 2x12's with an open back speaker above, and closed back below are great to run with different mixes into the two speakers if you have the gear to pull it off. Run one dry, the other wet and you have a nice wet/dry mix in the speaker. Run another speak on the other side of the stage similarly and you get your actual stereo separation from the two cabs but each has a nicely dialed in wet/dry mix.