The best fit is IBM. It's a domestic company with a long standing history. There would be obvious benefits to a merger such as this, so long as Moto doesn't file some suit alleging anti-competition (on chip purchases by IBM-Apple).
Sony is a Japanese company, BMW is German, Swatch is Swiss I think. The US Government takes technology transfers overseas pretty seriously, and there might be some interesting hangups with a purchase/merger by a foreign company. HP and Compaq had huge anti-competition and shareholder problems when they merged, so they are off the table. Microsoft probably can't buy Apple because of its ongoing federal problems. Gateway, nothing need be said. Motorola? That's the only wild card among the "obvious" potential purchasers/merger candidates.
IBM's huge enough, and like was said earlier, they make good products, but their industrial design sucks. They also use MS and Intel/AMD chips. Plus, they dropped their retail computer sales. This would allow IBM to again have fantastic well designed machines, control over the chips and OS, as well as a retail presence under a different brand name (similar to Old Navy/Gap).
Anyway, I don't think it will happen, but if it did, I'd say IBM is the most likely candidate.