This website, tidido.com, is most likely too good to be true (/legal).
You get millions of songs ad-free, subscription-free and it even works on mobile (even with the screen locked).
Not that I support it, you can even download entire albums by copying the URL to jDownloader.
And for the sing-a-longers, it's nice to have lyrics a click away (when available).
Update: It appears some artists have already been removed (e.g. Bob Marley).
Seems pretty good to me!