Short term plays have and were already taken ahead of the news so you've missed the boat. Longer term plays would typically have centerd around gas, but with excess capacity from the US and UAE and Saudi about to mix it with Qatar on a political basis you'd be crazy to attempt to deduce a way through to profit.
Putin has made a bold move and he would not have done so without a solid commercial a basis for doing so. Forget his need to protect the Russian military bases in Crimea, that was always a given and the West has seemingly given up on even thinking about wresting power from him there, quite sensibly too. The military build up while partly logistical to provide additional security for existing Russian bases, also serves as a smokescreen for the commercial aspects.
What the major players will be doing now is getting as much inside research data as they can get their hands on to find out what it is they (the Ruskies) have discovered about Ukraine and most likely that will be related to mineral assets.
