The Draw-Tite weight distribution hitch uses two pivoting spring bars
that get pre-loaded to oppose the torque imposed by the tongue weight.
This transfers weight from the rear wheels to the front, besides
leveling the hitch connection. If a side gust is encountered, causing
the trailer to yaw, spring tension will increase on the side of the
gust. The pivot points are offset from the ball, resulting in a
restoring (gust cancelling) force. A similar effect occurs when going
over dips or bumps in the road: pitching oscillations are also
reduced. More info is available at:

http://www.draw-tite.com/

Be advised that a full hitch can cost 500-600 USD, but I consider it
worth it. My wife won't drive the rig without it. You are also less
tired after a day of towing. Last week we had an 8 hour day of driving
and felt fine afterwards.

BTW: These hitches don't work for tubular tongues: they must be square
(AFAIK).