I'll try to compose a rough list of strategic importance myself based on criterions from DVK. Individual rankings as well as their wight to importance are simple guesstimates. Please comment you criticism.
Perspective is that of Russia / NATO interest because those are currently the only significant military factions in Europe.
Component lists:
Sea/land invasion route to/from Russia:
Russia, Norway, Ukraine, Sweden, Romania, Czech Republic, Azerbaijan, Austria, Serbia, Bulgaria, Slovakia, Georgia, Armenia, Denmark, Turkey, Finland, Estonia, Kazakhstan, Poland, Iceland, Hungary, Belarus, Moldova, Lithuania, Latvia
... Kazhakstan buffers against China, but it's excluded from discussion about Europe.
Can provide/deny sea access:
Russia, Ukraine, Finland, Estonia, Sweden, Denmark, Norway, Turkey, Spain
Nice islands from where to project power:
Iceland, Greece, Italy
Nice mountain range between NATO & Russia hearthlands:
Norway, Sweden, Czech Republic, Slovakia, Ukraine, Romania, Serbia, Bulgaria, Macedonia, Albania, Montenegro, Bosnia and Herzegovina, Croatia, Slovenia, Austria, Azerbaijan, Georgia, Armenia
High nominal GDP/area. Over 5 million USD / km^2:
Monaco, San Marino, Liechtenstein, Malta, Netherlands, Luxembourg, Belgium, Switzerland, United Kingdom, Germany, Denmark, Italy
I think my data was from 2012 CIA factbook (I did the numbers over a year ago). See visualization: https://dl.dropboxusercontent.com/u/2454917/map.png . Unfortunately large areas with lots of variance like US/Russia/China/Australia tend to average out a lot.
Moral:
Vatican
High net foor exporter after own consumption:
United Kingdom, Netherlands, Germany, Italy, Belgium, Spain, France
Energy exporter (oil/gas/coal/uranium):
High: Russia, Kazakhstan
Medium: Norway
low: Poland, United Kingdom, Netherlands, Ukraine
Metal producer (iron/aluminium/copper):
High: Russia
Medium: Kazakhstan
low: Poland, Norway, Ukraine, Germany, Sweden, Iceland
Composite list of strategic importance (grouping):
I don't know how to weigh any of the components properly, but here goes:
Russia
Largest single country on earth/in Europe. Attacking/defending Russia means there's a lot of land, sea, energy and minerals to capture/defend.
Kazakhstan & Norway
Both are rich in energy and metals, though Kazakhstan much more so. Then again Norway has a mountain range and is a possible (mostly) land route to Russia. Can close Baltic sea access. Kazakhstan buffers agains China, though not strictly an Europian interest.
Ukraine
It's a tried and true invasion route to Russia. Carpathians shield it to the southwest. Has Black Sea access (Crimea/Sevastopol). Also has some energy and metal resources.
Sweden
Sweden has mountain range between NATO and Russia. It's a possible land route to Russia. Can close Baltic sea access.
Iceland, Poland, Germany, United Kingdom, Netherlands, Denmark, Italy
Iceland is a good place to project power, it's and invasion route to northers Europe and it has some metal production.
Poland makes this category because it is on a convenient route to Russia and has some metal and energy production.
The rest are all high GDP density countries. With the exception of Denmark and Iceland, all have also a large food surplus.
Italy with it's islands is also a good place to project power from.
Denmark can close Baltic sea access.
Germany has some metal production.
UK and Netherlands have a little energy exports too.
Belgium, Romania, Czech Republic, Azerbaijan, Austria, Serbia, Bulgaria, Slovakia, Georgia, Armenia, Turkey, Finland, Estonia, Spain
These countries are on an invasion route to Russia (except Belgium & Spain).
They also have nice mountain ranges between NATO/Russia to defend with (except Belgium, Turkey, Finland, Estonia, Spain don't have any or aren't "in between").
In addition Finland, Estonia, Turkey and Spain are in position to easily block Russian sea access.
Luxembourg, Switzerland, Malta, Liechtenstein, San Marino, Monaco, Hungary, Belarus, Moldova, Lithuania, Latvia, Croatia, Bosnia and Herzegovina, Albania, Macedonia, Slovenia, Montenegro, Vatican City, France, Greece
Most of these countries have only one of the following to make them significant:
- easy invasion path
- nice mountain ranges to block land access.
- high GDP density
Also france is significant for high food surplus, Greece for nice islands from where to project power from and Vatican gets an honorable mention.
Portugal, Ireland, Cyprus, Andorra, Kosovo
These countries don't seem to be strategically very important.
Now comments please.