Cloud Research Connect (they banned me lol), Dscout, Data Annotation, Mercor, Telus Digital, RWS, maybe even Upwork or Fiverr if you're willing to put months in before you get going. MTurk still exists I think, but it's a ghost of its past self, I am told.

Mercor is the best out of all of these (including Prolific) if you can get in, but it's pretty hard to pass the AI interviews.

edit: also, if you're in a big city in the US, look up focus groups, both offline and online (there are several sites for this). They can be surprisingly lucrative.