What about some type of panfish like pumpkinseed and bluegill and maybe a few yellow perch. Bright colours, cold water, eats worms readily and you can still eat them if you get the hankering to try aquaponics down the road. I'd say 55 gallon tank minimum though.

I have raised all three in fish tanks which is what got me started with raising red wigglers in the first place. Sunfish as they get bigger tend to like foods other than red wigglers. My favorite native fish are darters. They tame easily, so to speak, and never grow tired of chopped red wigglers. Like mr yan says go with a 55 gallon aquarium. This is a popular size, and easier to maintain than smaller aquariums. Just get a good filter and change a littler water (about 10% to 15%) weekly. Personally I like the German canister filters for a 55 gallon tank.