These are my all time favorite restaurants in Cocoa Beach and vicinity (this is coming from a virtual native as I own a condo here):
Crab Heaven - 6910 N. Atlantic Ave., Cape Canaveral. 783-5001 Very, very casual but just about the best darn crabs you will ever have - the typical crab place that has brown paper on the table and wooden hammers and whatnot in the center of the table. It is casual vacation stuff and has outdoor dining. It is heaven for me and a must not miss every time.
Frankie's Wings & Things - 555 Glen Cheek Dr., Cape Canaveral. 799-4349. $$ This is at the port and has great oysters. Typical oyster bar just down right good food. Very, very casual again.
Then to go up in class - but remember you're at the beach I usually like to stick to my beach wear all day long - this restaurant is formal and is wonderful:
Mango Tree - 118 N. Atlantic Ave., Cocoa Beach. 799-0513. $$$$$ They have an amazing outdoor garden area and the food is spectacular. You do have to change out of beach wear for this one though.
That's my two cents of places that I go ever trip down to Cocoa Beach.