I have just written a simple tool to convert Chinese Sentences to their PinYin representations. It's here.
This tool work for both simplified and traditional Chinese sentences.
The original intention of this tool is to help me to convert my MP3 songs with Chinese file names to PinYin file names. For example, 一åƒé›¶ä¸€å¤œ will be converted to YiQianLingYiYe, This is because my car audio player cannot display Chinese characters.