As reported earlier, most of the the Lavamus network of sites are back up and running (Edit: it looks like downloads are working too, as reported in the comments below) - that includes iSound, Lavamus, and MP3Legal. These sites are all basically the same music provider, just with different names and usually the same music catalog. That is not entirely the case with all of them, though: JustMusicStore has a somewhat different (much larger) catalog; however, it is not back online yet. It looks like they are re-setting up their server : the default Apache page is currently showing if you go to their site.
I am guessing that JustMusicStore is coming back online sometime soon, but I don't know how soon it will be. The recent re-appearance of these indicate that it might not be far off. If you want to read a review of iSound, Lavamus, or MP3Legal, please check out the iSound review - they are all similarly priced and probably have exactly the same catalogs.
If anyone uses these sites and has any comments to make about the service now that they are back online, please feel free to leave comments here.