Not much for now, but these can be useful:
 

The Utopia Team
In terms of support and information, these guys do it much better than me. They also coordinate the new driver development effort and have made a soundbank for the PnP which seems to be quite good! Pay them a visit if you have any more questions concerning your GUS or PnP.
http://utopia.a1.nl
 

The GUS digest
This is not a link, but a pointer to the daily GUS digest which still works, but does not have the volume it used to back in 1993. ;-)

The GUS Digest:
To post to tomorrow's digest:
        <gus-general@mail.GAIANET.NET>
To (un)subscribe or get help:
        <gus-general-digest-request@mail.GAIANET.NET>
To contact a human (last resort):
        <owner-gus-general-digest@mail.GAIANET.NET>
 

Walnut Creek CD-ROM
The repository of native GUS software. These are old, but can be useful.
ftp://ftp.cdrom.com/pub/gus
 

The GUS FAQ
It's as close to a relic as it can be, but it still has some interesting information.
http://src.doc.ic.ac.uk/packages/ultrasound/info/gusfaq.txt.v2.02
 

The GUS MIDI FAQ
Ditto for this one, but it can be useful also.
http://galaxy.uci.agh.edu.pl/~polak/midi/gus.html
 

GUS Open directory area
The Open Directory Project has an area dedicated to the GUS.
http://dmoz.org/Computers/Hardware/Components/Sound_Cards/Gravis_Ultrasound/