I can think of more than a few times that this has happened. Finding a new friend to lead me to Jay's Getaway in Morgantown, West Virginia. Randomly picking Magic Hat's American Sour, and loving it. Two of my favorite memories. But the one that I will talk about, is what I consider one of the best deals that I have found.
My worst kept secret is that I love Max's Taphouse. It was my go to beer bar (as it is with many other people), and it formed the beer geekery that I now employ. They have some great specials, usually posted on a chalkboard across from the main bar (if you never have read it, you must when you walk in). Special 12 ounce bottles are usually on special for $3.50 and "Big Bottles" are usually priced at $5. And I just happened to run into Stone's Vertical Epic 09-09-09 on the Big Bottle list.