BDSM came first for me, but that may just have been because that's what presented itself first. The same person that introduced me to BDSM took me to my first orgy, so I've been pretty open sexually since I was 16.
BlackIce, there are three sites that I've found (although there are MANY more out there).
LoveVooDoo,
Playful Swingers, and
Swing LifeStyle (or SLS) are good sites. I've met the most people on SLS. When my bf and I were together, we were looking for a single female, and couldn't find one in our area, so when we broke up, I decided to become the single bi-female. Sometimes, you just luck out and find people. I've been with at least 15 couples in the last 3-4 months, and most of those I've been with more than once, just because we have a good time together.