Hello Feld...
Any of the algae wafers will do, but I don't feed those very often. I feed a variety of frozen foods. They have no additives, so are good for my fish. Frozen brine and Mysis shrimp, plankton, bloodworms, beef heart and krill are all good for your Corys.
I don't feed very often though. A couple of frozen cubes dropped into their tanks a couple of times a week and a wafer once or twice is all they need. They're foragers and spend their time moving gravel around, hunting for the leftovers in the tank and eating the algae from the plant leaves. Make them hunt for their food and they'll stay nice and healthy. I have some Corys that are several years old.
B