I need some more stuff to put here. If you have anything I can put here, I'd be glad to hear it!
Russia
& Britain:
My best unexpected trick is with Russia. Do you know your sub and transport in Karelia's sea zone? Keep it there along with both of your fighters in Karelia. If at any time Germany has maximum six or less units defending at 2 in Germany, start this plan with the beginning of the U.K.s turn. First thing that must happen is the Britian sea zone and the Baltic sea must be clear of German ships. Have Britain send fighters after subs and transports in those two sea zones. Next, have British bombers fight to the death over the skies of Germany. Remember, there is no comfort zone for this operation. If you're lucky, you've probably taken out all opposition except for maybe two tank divisions.
Next, Russia's turn comes around before Germany's turn. Russia loads two infantry into it's transport, and takes it around for a direct attack on Germany. Also, take the two fighters in Karelia and attack. If you're unlucky and one gets shot down, then just hope you've chisled their defense down enough. Use standard attack combat logic and lose one infantry, then lose fighters.
This trick works with American transports in eastern Canada sea zone to possibly play the part of Russia if they've run into some bad luck, though Russia is much more surprising, I've found and Germany usually gets suspicious when America moves transports within range of invading Germany.