Hmm... lets see..
Crappie and Bass.. light, firm fleshed, freshwater, clean tasting..
If you have a smoker, fire it up... rub a little olive oil and the spices of your choice on the fish, and smoke it..
Ceviche is certainly possible, there is a mexican restaurant near where I live that does ceviche with catfish, lemon, and cilantro; however, I would be wary of noncooked freshwater fish. Note that sashimi is, pretty much without exception made from saltwater species. If someone can come up with examples of raw freshwater fish used in Japan, I'd love to hear it, as well as love to hear what to look for in regards to freshwater parasites, but I'd bet dollars to doughnuts that its not done, or not done much.
One beautiful thing you can do is simmer the fish very gently in white wine, with some lemon and pepper. Adding minced garlic would be a nice touch.
I would avoid red wine, as it may overpower the fish.
Herbs are a great thing. Lots and lots of herbs. Cajun seasoning and a little olive oil mixed together and rubbed on, then popped under the broiler is good. The same can be done with fajita seasoning.
You might look up a recipe for a New England Boiled Dinner as well, and see if you can adapt that to your liking, lots of fish and veggies there.
Back to the Japanese, miso paste is great - both as miso soup, and spread onto fish in a thin layer on one side, before you broil, is also outstanding.
or... Poach the fish in dashi, remove the fish, add udon noodles to the broth, cook an egg in with it if you want, maybe some seeweed or other veggies that strike your fancy, then return the fish to it and serve.
I hope these suggestions, in addition to the suggestions of others here, will get you on track towards a more varied preparation of fish.
Chris
Chris Holzman
Moniteur D' Armes USFCA/AAI
River City Fencing Club