I have lived in our house for two years, and almost every day there is a great memory. I've lived on the main floor both those years - only ten of us in five rooms there, so we were all very close. I love all of our late night movies, study sessions, and talks, and it's fun when all ten of us are crowded into the bathroom getting ready to go out.
I think my favorite house memory is a little tradition we have just for the girls in the house: At 2am on the night after our "Pi Phi Christmas" party, the seniors come around with (battery powered) candles singing Silent Night, wake us all up and gather us all into the living room. There, the president reads "The Littlest Angel" and we sing Christmas carols while enjoying cookies and milk. It's a fun time of sisterhood for the in-house girls.
But really, the best things that happen in the house are just the friends you make when you live so close to all your sisters.