I still have at my store a couple of Generalmusic WK2arranger modules. These can play midi files direct from floppy disk or you could install an internal hard drive for playback. These are Italian made units which have been made for the past 6 years and have been discontinued because sales of modules are not nearly as popular as keyboards. You can manipulate tempo's, keys, sounds, etc. You can even use the built in video interface to show words of midi file songs on a TV screen.
Price for these used to be over $1000.00 and I have a few new ones left at $795.00.
I also have the Ketron XD3 which would do the same job but for a price of $1500.00. This is also made in Italy. Ketron also makes the Midjay as mentioned above by someone else but also sells for over $1500.00.
Yamaha makes a little box called the QY100 which is the size of a video cassette and can have midi files loaded on a smart media card which can be loaded into the QY100 to playback songs, but this is quite a small box with very few buttons so there is a lot of complicated button pushing to get things to work and sells for $499.00.
Roland and Korg no longer make anything.
George Kaye
Kaye's Music Scene
Reseda, California
818-881-5566