Some of the greatest moments have already been covered in this thread.... so rather than repeat the same great ones i will add 2 games that were awesome, only because they were both victories over the eagles and i have been forced to watch many games as the only cowboys fan in a room filled with eagles fans.
One game came when the Boys were not having such a good year, i think aikman might have been the QB. Anyway, the Boys defense pulled a big upset win over philly and i think they had some rediculous number of sacks that game, at any rate, philly had the number one ranked defense that year and all i heard sunday morning was how bad the boys would get spanked. After the game one of the cowboys defenders was saying "who played like the number 1 defense today" over and over again and i was totally rubbing it in the eagles fans face because they were doing so much trash talking.
The other one would be Emmitts first 100 yard rushing game against the eagles which to me marked the changing of the guard before the first SB with aikman, emmitt and irvin. After that game i called this one friend of mine who had been totally on my case for the previous years whenthe eagles beat the cowboys and his reply was classic "well, you can laugh all you want, it doesnt hurt me because im not an eagles fan anymore, in fact i just think football's a stupid waste of time anymore, so i guess you really cant rub it in, too bad for you". that just made me laugh harder.