1. Galicia (affects A and R right off the bat, affects how A, R, and T deal, and all this indirectly affects how G and E will deal with R, given how powerful or not it is and where it concentrates its forces, and how I might deal with A and R...really on F is a bit of a stretch here, so with 6/7 affected, I'd say it's #1)
1. English Channel (a move there by either E or F and the West erupts into war, if it's successfully DMZed E and F and, for a while, perhaps even G are free to go Eastward in a Western Triple or at least an E/F Alliance; this really effects the West, and can have a great impact on the East.)
3. Venice/Trieste (I'll cheat here and go two for the price of one for the obvious reason that they're so linked in the game in terms of importance and who likely owns them that really they almost can count as one...DMZed and a likely-strong A/I Alliance can really hit both sides of the board, one side could take Venice/Trieste from the other and that one power, then, can quickly take the other and itself become a power in its region, if not a Board Power, or there could be many turns of bounces and wars there, effectively making for a weak middle and giving the corner powers a greater chance at power.)
4. Black Sea (I'm surprised this hasn't gotten more fanfare...either there's a war there and the whole East from R to T could become weakened and vulnerable, one side takes it and weakens the other until they're out or a non-factor, thus affecting plenty of other nations, or, of course, the always-trumped-up possibility of a true--at least fpr a while--Jugernaut.)
5. Belgium (My highest-rated nuetral here, and as its a center G, F, and E all want desperately and can decide so much on who in the West will emerge as the power in that region speaks to its place here...)
Honorable Mention: Munich (Important, and you arguably can't win with most nations without it.)
Underrated Center: Greece (I think this center is short-changed in this sort of a debate, hasn't made hardly any lists so far...and yet it's BIG for I, T, and A, possibly for R if he's gotten that far, and, interestingly enough, in my experience E and F can really care about that center, as though they might not have it their ENEMY out of the east with a large armada--usually T, sometimes I--can have that center and they tell the other power, I or T, sometimes I to take it, to cut the flow to the Ionian Sea, which DOES get a lot of reputation here, and not unduly, but Greece to a great extend dictates who can hold not only the Ionian Sea, but the Mediterranean Sea Spaces as well.)