A lot depends on the skill level of the players. Assuming that the players will be roughly the same skill level, how about:
Russia–-Trans-Siberian Railway (quicker defense/attack response)
Germany—Panzerblitz (allows greater use/mobility of German armor)
United Kingdom—Mideast Oil (allows greater use of aircraft, ftrs can attack Med. and return)
Japan—Lightning Assaults (allows rapid attack of coastal areas)
America—Mechanized Infantry (allows greater mobility/attack)
If you allow more than 1 national advantage each, stay away from Superfortresses for USA. It makes the game pretty lopsided. IMHO the same restriction applies to Banzai Attack for Japan.