I'll start it off! Just about three years ago I started a niche sex tube and in three months it ranked 6000 in the world and was getting over 15,000 uniques a day!
Sadly I really didn't know crap about IM at the time and sold it to someone who did. I got $20,000 for it on eBay and thought I was the king of the internet.
I got an email from the buyer saying he was looking to sell and thought it only right to ask the original owner (me) if I'd like to purchase it. The asking price $250,000. I thought he was joking and told me that he did nothing to the site since he bought it and only knew how to monetize it, and monetize it he did. He was getting between $500 and $700 a day, everyday!
When I owned it I was making $3 to $5 a day...Dohhh!
Anyway this is the one that got away.
Anyone else like to share?