Art of Travel - How to see the world on $25 a day or less
Footloose and Fancy-Free in the Third World - Randy Johnson's online travel guide
World's Cheapest Destinations - Tim Leffel
The Gap Year Book (very skewed towards UK travelers) - By Lonely Planet. Try Rough Guide's instead...
First Time Around The World - Better RTW book by Rough Guide
Trip Spot Travel Books - Browse all travel book series
Read This First - Lonely Planet Series on general regions of interest