Meat - The objective in reheating meat is to get it to an internal temperature of 165. Although all meats heat at separate temps and times, an easy way to meats is to put chicken or beef stock in a pan and bring to a simmer. Add your meat and cook until it reaches 165 internal temp. For thicker cuts of meat, cut it no thicker than 1" thick. Plan on 20 minutes of reheating time for a 1" thick piece of meat.
Pizza - Throw it in the microwave JUST until the cheese melts (about 1 minute per slice), and then place on a nonstick fry pan on the stove set to medium high heat until the bottom is crispy (3-4 minutes)
Soup - The meat and veggies in soup tend to absorb liquid while they're in the fridge. Microwave on high power, stopping to mix every two minutes. Add fresh stock (beef, chicken, or vegetable stock works well). To liven up the soup, add some citrus juice.
Pasta - The key to reheating pasta is to store the sauce separately from your noodles. Put your noodles in a covered vessel that will still allow steam to escape. Add 1/2 cup water per pound of pasta, and microwave until steam starts coming out of the vessel. Let sit in your microwave with the lid on for a couple of minutes. Add fresh basil to your sauce S;
Mashed Potatoes - Cook in the nuker on 60 second intervals, stirring well after each time period. Add additional liquid as you cook until your potatoes are creamy.
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