I once saw two players get heads up after a preflop raise, hit set over set on the flop and check it down. The board went 3-flush on the river. I think they were both slowplaying each other and then both got scared when the flush hit. (Either that or it was collusion.)

One that stands out for me simply because I was in it & I think I posted the hand,

6 handed LHE... UTG folds, MP limps in I raise with the button cold calls BB calls 4 of us take the flop.

Flop cpmes out BB leads MP calls I raise it button calls 2 cold again and BB just calls

Turn BB leads and between me and him we cap it with the other 2 guys still come along for the ride.

River BB leads, now MP wakes up and raises I 3 bet (button finally decides his hand is no good and folds), BB caps it and MP calls the cap.

BB had for a flopped straight flush & I suck out on the river to give him the sucker straight flush. MP had the for an A high flush.

Probably be a while before I see someone flop a straight flush and then someone hits a 1 outer on the river for a higher one.