Let's see, there's a few.
Fighting in the Karma War was definitely one of them. It was the culmination of a couple of years of being under the NPO jackboot in various ways(mainly through their sponsorship of Nordreich and Norden Verein), and it felt lovely to get revenge for it. Also, it the first time I was on the winning side in a major war, which is kind of ridiculous because I'd been playing for three years at that point.
Also, fighting almost to the bitter end with SWF in GWIII. Never has an alliance gone down in flames against so bitter a foe quite like that. Really, me fighting the fascists in all the ideological wars was full of proud moments.
Oh yea, also fighting with MK in the Unjust War. Kinda wish I could go back some times, haha.