I just finished "Hell's Half Mile: River Runner's Tale of Hilarity and Misadventure" by Michael Engelhard. It's got some great stories in it. I also agree that Cadillac Desert, Sunk Without a Sound, The Doing of the Thing and There's This River are River Classics as well.
I also have an old dog-eared copy of "No Shit, there I was" volume 4 with a couple of great river stories in it - I take them on every river trip. There's a story about a guy who takes his family on a Dolores trip that is priceless, so, if you ever come upon a copy, I heartily recommend you grab it