Provided courtesy of:
Oriental Outpost - Asian Art Gallery
Enter Hanyu pinyin in the form like "ke4 zhou1 qiu2 jian4", and the output of Pinyin with tone diacritics like "kè zhōu qiú jiàn" will result.
You can paste those results into a word processor, or a webpage (though using UTF-8 encoding is recommended on any webpage where you want these to be displayed correctly).
This program can handle over 10,000 words (Chinese syllables) at a time!
If you are doing a bulk/large amount of text conversion: Just paste it in, and click submit. Then put your cursor in the output box, hit Ctrl-A and Ctrl-C to copy everything, and paste it into your word processor, or wherever you need it.