Several of the races encountered by SG-1 have mastered the use of gravity field generators in order to control, alter, or artificially create gravity. The Nox possess the technology to build entire floating cities. The Asgard have also built cities with stations and ships that hover overhead. The Asgard life support pod aboard Thor's vessel generated an anti-gravity field which allowed it to float and made it easy to move. Most spaceships, from the Asgard motherships to the Goa'uld scout ships, alkesh, and pyramid ships, require inertial dampeners and artificial gravity to limit the effect of G-forces and make normal movement aboard the ship possible while in space. Even Earth's own ships such as Prometheus and Odyssey are equipped with artificial gravity. Escape pods, such as those used by the Goa'uld and Tok'ra in scout ships, use anti-gravity wave generators to slow descent.
Among the Goa'uld, Ba'al possesses the most advanced level of anti-gravity technology. On Erebus, the prison world under his domain, an anti-gravity dry-dock was used to construct a ha'tak vessel in midair. Most sinister was his secret outpost which had been a test facility for weapons technology and gravity field generators. There his successful manipulation of gravity gave him the ability to alter the direction of gravity at will, an advantage he used in maintaining prison cells and administering torture. O'Neill had been imprisoned and tortured by Ba'al at this secret outpost, but was able to escape when the facility was attacked by Yu and the gravity field generators were destroyed.
Cross Reference: Asgard, Ba'al, Erebus, Gravity Cell, Nox
Episode Reference: The Nox, Abyss, Orpheus