Hi Crazy,
I've heard good things about
Adult Friend Finder, although it is not a poly site per se, poly people have had good luck with it in the past.
FetLife is not a dating site, but it can be a good place to find poly groups and poly people.
Poly Matchmaker used to be pretty good too, although like OKCupid, it has gone downhill in recent years. Honestly, dating sites in general are a long row to hoe. Your odds are probably better when you look for poly people in real life.
Even if it's not an "alternative" type group, if there's a club or something in your area that does something you're interested in, you can always join that group and it just gives you a way to get out there and meet people. If you meet someone on a platonic level and get to talking about poly, then they can decide how they feel about it without any "pressure to agree." Then if they do decide poly doesn't bother them too much, and some kind of romantic connection subsequently develops, you'll already have "had the poly conversation" with them.
You can also look for local poly groups in your area. Just google "polyamory" with the name of your state or nearest major city, and see what turns up.
Regards,
Kevin T.