Mine is a Pikachu Promo #1. But is not a normal promo. It was a promo card that I pulled in a Jungle booster a long time ago. I thought it was just another card in the Jungle set until one of my friends pointed out that it had a "Promo" star. I was astonished to learn that the card was extremely rare and was found in approximately 1 in every 10 boxes of cards (possibly even more rare).
Considering that I almost never see it on eBay nowadays, the original hypothesis seems to hold true. Ranges of prices for this card suggest anywhere from $50 to one particular auction on eBay where it sold for $1000. I doubt it will fetch a price that high these days. I know that the promo card given to the champion of last year's Worlds sold for over $6,000!
I think Andyman, if what he is saying is true, has the most priceless and unique card in this thread. There isn't anything that is like it out there. If I had a card like that, I would hang onto it for a very long time because it would have more value to myself than monetary value.
EDIT: Scan of promo added