Anything by Kurt Vonnegut! OK, so he's not a travel writer per se, but his characters do end up in the strangest of places. PLus he's great fun to read, even if you do end up feeling like we're all going to hell in a handbasket. A fun handbasket, though.
I'd have to agree with "The Hitchhikers Guide" as it is actually what I'm planning to bring when I go RTW in 4 weeks.I also found "The Gringo Trail" pretty inspirational as was Ewan McGregor and Harry Boormans "The Long Way Round" probably cos they are the last two travel books I read.
There is a serie of novels that come to my mind, originally written in French, but who knows, maybe translated: "La Bicyclette Bleue" by Régine Déforges. The reader follows the hero (a woman) through the World War II in France in the first book, then to Argentina in the second book, Indochine (=Vietnam) in the 3rd, Cuba in the 4th, and Algeria in the 5th... *of course* there is plenty of romance, war, and crying in every pages...
Now, that's what I call travelling through time and around the world!