Which items have you never heard of?
Aluminum (only 12 are known to exist! they made 1.5 million, but trashed em after a long debate...wtf? true story lol
Modern Half Dollar (they sell em through the mint...so you don't see em often in circulation)
They make em of Silver Plated, Pure Silver, Platinum Plated and Pure Platinum. (They can literally be spent as $1, but you'd have to be a complete idiot, since they all cost a shit load of $$$$$$s