I agree with Seth. I find cold pizza to be gross too... Then again I don't like pizza to begin with...
For me, it depends on what the leftovers are. Breaded chicken is always better when it's first finished cooking. If you try to heat it up later, it just doesn't taste the same. You could eat it cold, although personally I like it better warm.
Pasta as a leftover depends on whether or not it has any condiments on it while it's in the refrigerator. Heating it up with Parmesan on it makes it taste funny in my experience. However, plain pasta is perfectly fine to heat up. I actually make an entire box of pasta just for the sake of being able to have some later.
Gravy, in my opinion, should never be saved. It never tastes quite the same after it's been allowed to cool off that much, and frankly, even if you heat it up again it still doesn't taste good anymore. That goes for whatever is in the gravy too, like meatballs or pieces of sausage. I never like those as leftovers. However, if the meatballs and sausage were not saved in the gravy, then I'll happily eat them as leftovers. For whatever reason, cold gravy seems to make things taste worse. At least, in my experience.