I don't know if this counts, since I wasn't on board, but it's the one I certainly remember most vividly.

I was staying at the Reno Hilton, which is located just northwest of the departure end of runsways 34R and 34L at RNO. I always try to get a room facing the airport, as it is great for plane-watching. It was a fairly warm summer afternoon and a NW 727 began its takeoff roll on 34R from the south end of the runway, heading toward me. Even on a warm day, with an 11,000 foot runway, most aircraft lift off with at least 2000-3000 feet of runway remaining.

Well, this 727 keeps rolling and rolling and rolling - as it fails to lift off, for about 5 seconds I am sure I am about to witness a full-fledged commercial airline crash. Literally with about 500 feet of runway left, the nose comes up and the main gear come off the runway with less than 50 feet remaining and barely clear the lights at the end of the runway.

It took me about 10 minutes to regain my composure.