My husband and I met in a class in junior high when I was in 7th grade and he was in 8th grade. We didn't start dating until the end of my sophomore and his junior year in high school though.
My boyfriend and I met last year at a friend's Halloween party (though until he showed up he had no idea it was at a guy's house that he had just spent a year in Iraq with). A girl my boyfriend was casually dating invited him after he texted her that his plans had fallen through for the night, apparently telling him it was an orgy. Which is funny, because other than a vacuum bed being played around with in one of the basement rooms, it was a relatively tame party. He gave me his phone number and, since I had enjoyed kissing him the night before and decided to see if he was my type at all, I texted him the next day to try to find out more about him. We got together for coffee two days after the party and have been seeing each other a couple times a week ever since, except when one or the other of us is out of town.
The good majority of other people I've dated I've met at the local polyamory support group. They've caught my eye at meetings so I've usually been able to find them on OKCupid and ask them out. One person lived in South Carolina and I met him on polymatchmaker.com. Another person I met at parties hosted by friends from the poly community. I have met a couple people on OKCupid but both of those I only went on a couple dates with before it fizzled.