The key to great onion rings is to use vidalia onions. Slice the onions, separate the rings, and soak in buttermilk. Out of the buttermilk and dredge in flour then off to the grease. Once they come out hit them with some Lawry's season salt, Tony's, or whatever else you like. Get a nice light, flaky ring. Simple and tasty. Much better than heavily coated, crusty, tasteless rings which are typical.
Crappie and Walleye are excellent sautéed in butter and hit with a little Old Bay.