Guide Books
First, anything from Lonely Planet is good in my opinion

Art of Travel - How to see the world on $25 a day or less (web-based!)

Footloose and Fancy-Free in the Third World - Randy Johnson's online travel guide (web-based!)

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

Vagabonding: An Uncommon Guide To The Art Of Long-Term World Travel - Rolf Potts 

Trip Spot Travel Books - Browse all travel book series

Read This First - Lonely Planet Series on general regions of interest