The most treasured gun I own as of now would be my Ruger 10/22. That rifle has killed more pop cans than a recycling center. Awesome little gun, and fun to shoot.
The one gun I will inherit from my grandfather is his old Sears & Roebuck 30-30. It's taken down many large Virginia whitetails and I will always remember him carrying that gun up and down the hills. Once I get a hold of it, not another bullet will be fired through it.