Listmania!
"I Took Yuh Fer An Injun" the Mountain Men, 1820-1840
By an Amazon.com customer
Firearms, Traps, and Tools of the Mountain MenFirearms, Traps, and Tools of the Mountain Men by Carl P. Russell
Buy new: $15.61 / Used from: $9.97
the late Carl P. Russell's magnus opus. It's required reading for the era
Crow Killer: The Saga of Liver-Eating Johnson (Midland Book)Crow Killer: The Saga of Liver-Eating Johnson (Midland Book) by Raymond W. Thorp Jr.
Buy new: $11.16 / Used from: $5.98
Some say it's truth, some maintain it's fiction. Either way, it's great reading on ole Liver Eatin.
First Man West: Alexander Mackenzie's Journal of His Voyage to the Pacific Coast of Canada in 1793First Man West: Alexander Mackenzie's Journal of His Voyage to the Pacific Coast of Canada in 1793 by Alexander Mackenzie
Buy used from: $225.00
this man predated Lewis & Clark in the area by 12 years!
The AssiniboineThe Assiniboine by Edwin Thompson Denig
Buy new: $19.95 / Used from: $13.91
anything by Edwin Thompson Denig is worth it weight.
Five Indian Tribes of the Upper Missouri: Sioux, Arickaras, Assiniboines, Crees and Crows (Civilization of the American Indian)Five Indian Tribes of the Upper Missouri: Sioux, Arickaras, Assiniboines, Crees and Crows (Civilization of the American Indian) by Edwin T. Denig
Buy used from: $11.49
again, Denig.
INDIAN LIFE ON THE UPPER MISSOURI (Civilization of the American Indian Series)INDIAN LIFE ON THE UPPER MISSOURI (Civilization of the American Indian Series) by John , C Ewers
Buy new: $21.95 / Used from: $9.24
Mr. Ewers is dead now, but his valuable work lives on.
The Fur Hunters of the Far WestThe Fur Hunters of the Far West by Alexander Ross
Buy new: $24.95 / Used from: $18.95
primary source: Alexander Ross.
Fort Union and the Upper Missouri Fur TradeFort Union and the Upper Missouri Fur Trade by Barton H. Barbour
Buy new: $24.95 / Used from: $14.99
recent work on Fort Union-upper Missouri.
Reconstructing Fort Union (National Parks)Reconstructing Fort Union (National Parks) by John Matzko
Buy new: $45.00 / Used from: $7.80
a great companion volume.
The Fur Trade on the Upper Missouri, 1840-1865The Fur Trade on the Upper Missouri, 1840-1865 by John E Sunder
Buy new: $24.95 / Used from: $6.83
again, required reading for time and place.
The fur trade: with concluding chapters by J.W.SmurrThe fur trade: with concluding chapters by J.W.Smurr by Paul Chrisler Phillips
Buy used from: $38.59
good luck finding these two volumes outside a library. I paid $100 bucks for mine, 15 years ago. U of Oklahoma publisher, but even they no longer have them in print.
Mountain Men and Fur Traders of the Far West: Eighteen Biographical SketchesMountain Men and Fur Traders of the Far West: Eighteen Biographical Sketches
Buy new: $13.57 / Used from: $0.99
In print.
Fort Laramie and the Pageant of the West, 1834-1890Fort Laramie and the Pageant of the West, 1834-1890 by LeRoy R. Hafen
Buy used from: $2.07
Recent trade paper from U. of Oklahoma: Press
Fur Traders, Trappers, and Mountain Men of the Upper MissouriFur Traders, Trappers, and Mountain Men of the Upper Missouri by LeRoy R. Hafen
Buy new: $12.55 / Used from: $5.94
In Print.
Trappers of the Far West: Sixteen Biographical Sketches (Bison Book)Trappers of the Far West: Sixteen Biographical Sketches (Bison Book)
Buy new: $29.95 / Used from: $0.98
In print.
French Fur Traders and Voyageurs in the American WestFrench Fur Traders and Voyageurs in the American West
Buy new: $29.95 / Used from: $15.00
In print.
Across the Wide MissouriAcross the Wide Missouri by Bernard DeVoto
Buy new: $12.21 / Used from: $3.06
Classic. Still in print.
Tabeau's narrative of Loisel's expedition to the upper MissouriTabeau's narrative of Loisel's expedition to the upper Missouri by Pierre Antoine Tabeau
Buy used from: $149.83
Hard to find, but still available.
William H.Ashley: Enterprise and Politics in the Trans-Mississippi WestWilliam H.Ashley: Enterprise and Politics in the Trans-Mississippi West by Richard M. Clokey
Buy used from: $2.53
If you've read all the books I've listed, you deserve the honorary  title "mountain man/woman" yourself.