MFX always have outstanding soundtracks to their demos, luckily quite a lot of them have been captured on YouTube. (or get their back catalogue from pouet.net) They're the best demogroup there is these days. (imo)
In the early demoscene there was a BBS-like system in England called Compunet. It was very popular with the mid-'80s demoscene and games industry. Several legendary artists from that time regularly contributed (such as Rob Hubbard, Tony Crowther and Jeff Minter) as well as some of the great sceners making their first steps. (such as Demon, The MIghty Bogg and Stoat & Tim)
A few of these early demos were interactive, a feature that sadly has been lost over the years. I thought I'd post links to them here if anyone's looking for some cheap way to do visualizations on their c64.
Wings, Mindwalker (amazing soundtrack), Sinbad:Throne of the Falcon (ditto), Hard'n'Heavy, Datastorm (great Defender/Dropzone mash-up) Clown'o'mania, Battle Squadron, Hybris, It came from the Desert, Galactic.