Due to the U.N. I doubt any of these wars could really happen. Also due to the development of nuclear weapons, large moving and occupying armies aren't necessary anymore. As was show in the Iraq conflict, quick and decisive attacks on infrastructure and personnel can really disable a country very quickly. But as all of you I am going to come up with who I think would win and why.
Germany vs. France. Germany is my obvious choice if they were the attackers. With them not buying into the euro they have a much stronger currency value, and probably the most stable economy in Europe. If France were the attackers although if they were quick enough could overwhelm Germany before Germany could arm themselves.
USA VS. China. This one could be just destroy the world. Imagine how the world would split itself. We see two large super-alliance of China, Iran, North Korea, possibley India. While for the US we would see US, Israel, most of Europe. Africa would play a very small role in this war as a whole. I see a large seawar in the Pacific Ocean headed between China and the US, and a large war taking place in the Middle East. In the end I see the US winning. Though I see the worlds population going from 7billion to about 3-4 billion. Huge determining factor would be Russia. If they hit China from the north and the US was coming from the south is could be the end for China.
China vs Russia. Almost the same as was stated above.
USA vs Russia. impossible at the current date.
SK and NK. If the war sparked between the two again, I see SK pulling through in the end after igniting the war of China vs USA.
Spain vs. Mexico. Mexico, they've done it once, they can do it twice, Mexico would be predominantly defending and the drain on the Spainish supply lines could be to much to hold.
Japan vs. South Korea. South Korea, they are like the Asian version of Israel. They do not get messed with, you mess with them or threaten them they will mess you up.

Israel vs Egypt. Israel would win. Israel has been a stable country for fifty years. Egypt just emerged from a rebellion and revolution. Israel could roll right through them. The true matter is how to consolidate Egypt after capture. Juddism and Islam are very different religions.
Britian vs. India. Britian could win if they attacked swift and precisly. If a long war happened Britain could lose because of manpower reasons. India has around 900million people while Britain has maybe an eigth of that?
Swiss vs. Belgiums. Swiss overall. Much stabler economy. Nearly every man there owns a rifle or assualt rifle. The shere odds of them losing againest Belgium are nearly impossible.
Pakistan vs. India. Let them kill eachother off. Both cause way to many problems for the world.
Turkey vs. Iran. Turkey is neutral and not mention a large stronghold of the Islamic Religion. Iran is much the same, they have no chance at getting into a war againest eachother. If anything a coalition would be formed between the two.