My wife's spaghetti with Italian sausage - I could do it for 5-6 days straight.
Right behind is her chili & my cheesburgers, probably 4-5 days straight.
Cheese is a good answer, and not only could I eat it everyday, but I do. However, the sheer variety of cheeses necessitates a clarification of a specific type that one could eat every day, such as colourblindchameleon's "blue" assertion. And although I am never very far from a good "blue," I personally would choose a nice white, mild "American" cheddar--the perfect food!
However, as a main course, I would choose fried chicken. I could eat it at every meal for as long as you could serve it up.
Angel hair spaghetti with meatballs or sausage. I prepare the spaghetti, my wife makes the sauce (her grandmother's recipe), the meatballs (her mom's recipe) and the sausage. Sometimes we throw in some pepperoni. To die for!!!
That's another good one. My wife has just started making this, too. Also, another is my step-dad's(R.I.P.) old recipe for Shrimp Creole. I wonder if this is a guy thing. There are probably 10 dishes that I could eat for a week straight.
Shrimp and Crab. And THAT season is coming soon. Drop the trap, play 18, pick up the trap (dinner) on the way home and have fresh blue crabs. Then in Aug/Sep, while picking up the trap, throw the net a couple of times and we have fresh shrimp AND crab. Some things it pains you to kill but blue crabs are so mean that I don't feel bad at all.