There isn't anything quite like Sega Channel nowadays, you can either download games via Virtual Console or other kinds of things, or rent from Gamefly. I've also heard of Gametap, but that's downloading games onto your PC and playing them. Might as well get ROMs and emulators xD

There's probably other services out there too, but nothing where you can just plug something into your console like that xD I even miss the little loading screens and music! They'd have tips on all the games and other stuff you could read as well, it was quite unique.