If old PC parts still works when I decide to replace them, I generally keep them or give it to a family member.
I never sold an item before, at least on purpose... The only thing I ever sold was my old iRiver H120 MP3 player when I was giving MP3 player advice to someone over at HardForum. I simply recommended the Cowon S9 to someone and mentioned my old iRiver was simply collecting dust. Someone else inquired about it and I simply price it at $100 (bought at ~$240).