History of Chinese Romanizations
Excellent Comparison of various romanization systems
A Guide to Gwoyeu Romatzyh Tonal Spelling of Chinese
Library of Congress Romanization Guidelines and Pinyin/Wade-Giles Comparison Chart
Chinese Romanization Comparison Chart, organized phonetically
Chinese Transliteration Converter
Pinyin - EFEO (Ecole française d'Extrême-Orient) Table