I lost around $100 over night by placing a $1 ppc bid on a game-related term that probably only appealed to kids.
On a stock trading forum, people were discussing domaining so I slipped in my affiliate link to a cheap domain registrar and my post netted about $70. I wouldn't call it spam since I was contributing a recommendation to the registrar I was using at the time, and I was active on that forum.
One day I threw up a cut and paste of a comparison site (as supplied to affiliates of one of the CB offers) to an unrelated domain name where I wanted to show a guy how the code I was developing operated, and it converted to a sale from some random surfer to generate around $40.
Then there are the out of the blue $100 commissions from bulk buys via affiliate links that pay way less than this normally. The first time was for printer ink. They must have bought enough for a whole office building. Maybe my employers were tagged with a cookie after the HR dept. checked up on me?
These are the ones that stick in my mind.
My forum signature is under construction.