'Summit Fever' by Andrew Greig. Non-climbing Scottish poet gets co-opted onto an expedition to the Karakorum by Mal Duff. Beautifully written outsider's take on climbing and climbers.
'Kiss or Kill', Mark Twight. Bonkers collected articles by similarly deranged American alpinist. Kind of inspirational and repulsive at the same time.
'Learning to Breathe', Andy Cave. As much for the descriptions of working as a miner during the dark days of Thatcherite Britain as for the climbing stuff, which is also good.
'Conquistadors of the Useless', Lionel Terray. Genius and perspective, legendary French climber from 40s and 50s.
And all the classics – The White Spider, Void, and Psychovertical (not a classic, but mentioned already), some of Jim Perrin's stuff – 'The Villain', his biography of Don Whillans is good. Pretty much all the stuff in the Boardman-Tasker Omnibus.
And on and on… It's odd how mountaineering has such an incredibly rich literary tradition while mountain biking's culture seems to have been written (sic.) in ephemera like magazines and DVDs. It's an age thing I guess.