I'll get this started off with the ur-furry-dating-site,
Pounced!. It's basically the FA of furry dating - "everyone uses it", "it's free", and it's not actually very good. I've got an account, and I've made a few friends through it, but it's also technologically from the 90s and is probably riddled to shit with security holes. (Passwords have to be made up of /a-zA-Z0-9/)
The next competitor seems to be "FurryMate", but I can't imagine them as anything other than a scam: take a look at
their blog. Every single post has 70 fucking tags, the whole thing is very heavily "search-engine optimized", ad-heavy, et cetera.
I've also run into OtherkinDating and Furries-Extreme but I don't yet have anything pithy to say about those yet.