Oh man, NES, the memories...
When I was a weester, I vowed that one day I would own all the NES games I ever liked -- all the games I played at a friend's house, or rented for the weekend, or borrowed from someone...but could never afford to get for myself, as a kid.
It took me many years, but I finally collected all of them. They're not always the most popular games, or worth anything to anyone but me...but I have a big steel guncase filled with every single NES cartridge I ever loved as a kid. Some of them are from birthdays and christmases long since past, and others are from trades and ebay purchases along the way...but they all mean something to me.