There are a number of names being bandied about at the moment including Microsoft and Samsung. Samsung are one of the largest smartphone manufacturers in the world with handsets at multiple price points running both Android and Windows Phone. Other than the patent portfolio, which will be much cheaper if RIM goes under, RIM has no assets that Samsung would want.
Microsoft would appear to be more likely. After the partnership with Nokia a deal with RIM would certainly be beneficial and would give Microsoft a foot back into the lucrative Enterprise market as well as giving Microsoft access to a portion of RIM's 13% of the smartphone market. From a technology point of view I would expect that much work has been done internally on the move move away from the traditional BlackBerry infrastructure and the incorporation of ActiveSync into BES. If this is in place then the union of the BES install base with Windows Phone would be hugely beneficial to Microsoft. I don't think it'll be Microsoft though. There is another company that makes more sense. HP.
RIMs renewed focus on the Enterprise puts them on the same strategic course as HP. While the Palm acquisition was a total disaster RIM is different. It has a well managed supply chain, a large and loyal fan base equating to 13% of the smartphone market, strong Enterprise presence and and equally strong international presence and overall the firm is profitable. The sale of Enterprise servers from HP with BES installed and tight integration with BlackBerry mobile devices would give HP control of a key Enterprise widget.
It's my expectation that while RIM could be turned around management is no longer interested in this option. Personally I'm a fan of BlackBerry and I am hoping the firm is able to refocus without losing its character but if not then HP seems the most likely owner of one of the worlds most addictive devices.