There is a WordPress plugin called ScoreRender. Also there are several cloud services like LilyBin or WebLily but it is not really possible to embed their outputs in web pages.
There is an Area51 proposal for Music Typesetting (it is proposed to be LilyPond-specific but despite typesetting music with nothing but LilyPond for years myself, I suggest it being more generic). If you like the idea, follow it and spread the word!
