SCIFI.COM | Stargate SG-1 - Downloads - Screensaver
Screensaver made up of promo pics provided by

SCIFI.COM | Stargate Atlantis - Downloads - Screensavers
Screensaver provided by

SG-1.CO.UK - Screensavers
Excellent ones here.

Cheyenne Mountain Stargate SG-1 Screen Savers
Screensavers by Katana. Check it out!

Dedicated To Stargate SG-1 - Screensavers
Lots of screensavers at this site.
Go to 'Screensavers' in the menu. - Screensavers
Last I checked, there was one Jack screensaver and one RDA screensaver available.