I've got a few old Pokemon cards, probably not anything like Charizard that's worth much. I wouldn't be able to bring myself to sell any of them though, even though they just sit in a box in my bedroom.
I hoard things. Like a dragon. (Because I am one :P)

The closest I've come to ever selling a card was trading a Yu-Gi-Oh! card I never used for almost an entire deck. (The card was worth around Ł20, and a key part fo a deck someone else was building, so I got amost a whole working deck for the achetype I wanted to play from them.) Sadly, most of the cards in that deck are banned/limited now, so I can't use it much. :/