The most famous marketplace is definitely opensea.io which i think it could still use alot of improvement, because it is still quite difficult to find the exact looking one as what you imagine, and also there is no way you would know if you are buying an underpriced or overpriced NFT.
Other places would be the direct auctions and NFT specific marketplaces:
Cryptokitties - https://www.cryptokitties.co
Etheremon - https://www.etheremon.com
Axie Infinity - https://axieinfinity.com
Decentraland - https://market.decentraland.org/
Gods Unchained - https://godsunchained.com
Marblecards - https://marble.cards
Blockchain Cuties - https://blockchaincuties.com
Feel like i missed out quite a few other marketplaces, any idea which is it?