For those of us hosted at WordPress.com, there are multiple ways to include music in a post. the simplest is to point the WordPress audio player at an MP3 file.
This raises the question of where to stash the MP3 files. In a recent support forum thread, DZonson suggested the use of Google Pages. You use Google Page Creator to set up a site, upload the MP3s, put them on a page, publish the page, and you can then use the WordPress MP3 player at the MP3s.
I should note that GPC is part of Google labs, which is a place for projects “that aren’t quite ready for prime time.” GPC imposes space limits, currently 10MB on a file and 100MB on a site (but you can have multiple sites).