From time to time I avoid the ridiculously high prices of fresh fish by opting for the frozen variety (don't tell my husband). I've had success with Dagim's flounder fillets that come in a bag. I defrost them in cold water, pat dry with paper towels and fry in bread crumbs or a beer batter.
I tried Dagim's frozen sole fillets in a box and they were awful, I had to throw them out.
Beer Batter for Fish:
About equal parts beer and flour, add salt, pepper and other spices you might prefer, mix well and dip fish, letting excess batter drip off before frying.