Last week FoxyTunes rolled out a cool new feature called Signatunes that lets users add whatever music they're listening to as their e-mail signature. Users with the latest version of Foxytunes get access to a button that integrates into supported e-mail and blogging services. Clicking it inserts a small link that lists artist and song information. This link goes straight to the song's FoxyTunes Planet page--a helpful service that aggregates artist information from various music reference sources on the net, and in many cases includes a preview, or free streamed version of the track.
I had a go with it earlier today and came away impressed. Like the rest of the Foxytunes extension, Signatunes is highly configurable. You can pick out how you want the song information displayed, along with customizing the signature to say anything you'd like.