Rev is probably the most well known transcription site. Some others I'd mention are; Scribe, TranscribeMe, Transcription Panda and I'm sure there are a few other good ones.
One thing though, I wouldn't expect to make much money from transcription jobs. It may seem like easy money to some, but the content you have to transcribe at times can take hours just due to how hard to figure out all the words and figure out who is talking. It can be tedious.
For example. I tried out Rev, and I remember my initial job was like a few 4 min videos, each one took me about 20-30 min each. And each one maybe paid around $1 or $2. Which is next to nothing for the time I put in. So I quit Rev and haven't tried transcription sites since. I don't feel it's worth my time. And now with AI making an appearance in transcribing, we're going to see AI used more, in turn taking transcribe jobs away from us.
What I suggested doing though in the past, was to utilize AI for the initial run-through of content (video, audio clip). So you'd run that content through an AI transcription tool, which will do most of the work for you. You just need to make sure the words are correct and add any other filler content required by the site, like mention of pauses, illegible words, etc. Rev had rules on how they wanted the transcription to be, so don't just rely on the AI to do it all.