Great Pinyin reference site: http://www.pinyin.info/
Interesting locations within site:
Rules for using Pinyin: http://www.pinyin.info/rules/index.html Where to place the tone marks: http://www.pinyin.info/rules/where.html Converting tone marks to HTML : http://www.pinyin.info/unicode/marks3.html An ENTIRE BOOK on the rules on writing in Pinyin! : http://www.pinyin.info/readings/orthography.html
Pinyin and Bopomofo Chart