RiffStation and SongSurgeon
RiffStation and SongSurgeon can slow down music without changing the pitch. Riffstation can slow it down to half speed. SongSurgeon can slow it down as much you want and you can mark sections to loop over and over again, which I often need to get all the notes correct, and then you can set the loop to play a little faster each time so you can play along and wind up playing it at full speed. Try it yourself. It works great!