For those who want their Pinyin pixelated — for example, to help reproduce the look of text on an old mobile phone — there’s PixelPlay, which is free.
Text source: I very want your deceitful surface, Pinyin News, October 13, 2005.
Since my last examination of the selection at Google Web Fonts the number of font families for Latin Extended has reached 98 [edit: May 31, 2012: 188], with one new face capable of rendering Hanyu Pinyin with tone marks: Noticia Text.
Here are the Pinyin-friendly font faces at Google Web Fonts.
Serif
Sans Serif
For future reference, the font most recently added to the Latin Extended group is Ruda [edit in May 2012: Chau Philomene One], which doesn’t support Pinyin with diacritics (except, perhaps, through combining diacritics).
See also