"Big" can mean different things to different people and in perspective.
What size tank are you wanting to have?
Fish can be found in adult size from 3/4" to more than a foot - like up to 3' or Red tail catfish gigantic.
And whether they need to be in groups or kept individually.
Koi
Asian Arowana
FW Stingrays
Bichirs
Pike
Large types Silver Dollar fish
Tinfoil Barbs, over 12-14". Should be in a group
IMHO Clown Loaches are really beautiful. Ideally need a really large tank like min. 150G