Short Walk in the Hindu Kush by Eric Newby is good, though his later books are a bit wordy. And The Road to Oxiana by Robert Byron. These are old and now as much history as travelogue.
Tracks is good - they've just released the film, about 30 years later. Across the outback by Camel doesn't date.
I've read all of Bill Bryson but will certainly look at those others mentioned. Much appreciated.
I have real admiration for those who set off on adventures, being very unadventurous and rather cowardly myself. It is also fascinating to read about Britain through the eyes of travellers.
I think it was Gerald Durrell's books that first got me hooked on the genre, he is an intelligent, passionate and amusing writer.