Originally posted by monochrome Sigma comes to mind. It is a family-owned business and the founder-patriarch passed away last winter. Wouldn't that be interesting? Perhaps Olympus if the financial condition is ever truly figured out. Maybe Sony throws in the towel - they're bleeding money. There's more than one way to get the mirrorless mount everyone seems to think K-mount isn't.
I rather suspect they will acquire share by "investing" capital into Pentax beyond product development, and by reinvesting increased cash flow as Pentax grows. That won't start until 2014.
If a logical acquisition presents itself at the right price Ricoh may be willing to make that acquisition as well.
Acquiring Sigma would be interesting, but in the sense of a challenge because of the proportion of their product that supports camera brands other than Pentax. Sony's camera division would be more of a fit, I think, because it would hold out the prospect of acquiring dedicated video product, and MFT systems as well as the possibility of preferred access to CZ lenses. I'm not sure how Olympus's product line would fit with Pentax.
On the other hand, if one thinks about investment opportunities, Pentax could do well to get back into the medical optics area, although I dare say the terms of Ricoh's acquisition block them from that for a while yet, perhaps even under the Ricoh name. There are, of course, other high-end, esoteric photographic markets that might be challenged on price, just as Pentax has done to Hasselblad and Mamiya with the 645D. Although those are low-volume, they are also high-margin and can bring prestige that may attract customers to the lower-priced products, and eventual technology transfers down to those products.