I'm looking for some good disco music. I'm not talking about the Saturday Night Fever soundtrack, Gloria Gaynor's "I Will Survive" or Michael Jackson's Off the Wall. Is there any good underground disco music?

There's loads of great disco music that's far removed from the Gloria Gaynor/Bee Gees Stuff people today usually connect with the genre.

Check out producers like Cerrone, Boris Midney and Alec R Costandinos for the more eurodisco related sounds. Also consider looking at the catalog by record labels like Salsoul, Casablanca, Prelude and West End for a huge variaty of what disco had to offer.
This site should also come in very handy. It's the best of it's kind:
www.discomusic.com

Wow a reply finally.

Thanks a lot . I for sure check it out.

Check out the After Dark compilation (on the Italians Do It Better label).

It's outstanding.