No referral links here...
We (Alysha and I) were members of
http://www.SwingLifestyle.com for awhile, and weren't pleased. Not a great site, but that's just our opinion. We are still members of these sites, though:
http://www.sdc.com
http://www.swappernet.com
http://www.playfulswingers.com
PlayfulSwingers.com seems to have more of the people in our age bracket (30's), while we get bombarded by 60 year old single guys with the other two sites. But, overall, we have met many people from all three and would recommend all of them.