Cory Cats will eat algae wafers, but aren't good fresh algae-eaters in the aquarium. They will not touch your common types of algae like BBA, GDA, GSA, Clado, Rhizo....pretty much any algae seen in the aquarium.
Good algae eaters include:
BN Pleco: good for green spot and green dust. Grows to about 4.5", so good for most aquariums 20g and larger, supplement with algae wafers and veggies.
C. Siamensis (Siamese Algae Eater): good for BBA, Hair, Thread, Fuzz. Can grow to 5". Prefers to be in groups of at least 3. Therefore, shouldn't be kept in aquariums below 40g.
Garra Pingi: Relatively new algae eater. Size and tank requirements similar to SAE.
American Flag Fish: Good for Thread/Hair/Fuzz and BBA. Can be territorial/aggressive
Otocinclis Cat: Small, prefers groups of 3 or more. Good for tanks 5g and up. Eats GSA, GDA, and Diatoms.
Mollies/Platies: Will munch on Green Dust and Hair
Other: Amano Shrimp and Nerite snails eat pretty much any type of algae and waste. Great clean up crew.
Loaches, Cory Cats, FW Sharks, False SAE, CAE, and most other plecos are not considered to be "algae eaters". These are bottom feeders/scavengers and search for food, or in the case of plecos, are vegetation(i.e. plant) eaters.