How to make mashed potatoes??

Looking back, I see that Sam already sort of mentions both of these things...

For what it's worth, Cook's Illustrated says that for creamiest mashed potatoes, add the butter and mix it in thoroughly before adding the cream (they recommend had-and-half, actually). When added in that order, they say, "the butter coats the starch molecules, inhibiting their interaction with the water in the half-and-half added later and thereby yielding silkier, creamier mashed potatoes.". I use their method and it works beautifully.

One final thing, as long as you're going for maximum deliciousness and fat content is not an issue for you, mashed potatoes can take A LOT of butter.

If you want cheesy mashed potatoes, add a cup of grated cheddar or other cheese to the mixture after adding heated milk and butter.

My only addition to Sam's excellent answer is to consider using a food mill for the mashing.

Heat the milk and butter in a mug or bowl in the microwave before adding to the potatoes.

I really don't like whipped potatoes. That's just my taste tho...the puree whipped stuff just doesn't have enough body for me. YMMV. Well, unless you let Thomas Keller do it and put in a pound of butter to a pound of potatoes.

I agree with him at the beginning "Peel potatoes. Cut in half, slice the halves into 1 inch cuts. Put in a pot of salted water and boil (about 20 mins--test with a fork until tender).
Drain water...let it steam off a bit. "
Move potatoes to a new bowl. Put milk and butter in low in the pot. Grab ricer and rice potatoes into pot.
Use hand mixed to whip potatoes!
Absolutely the best potatoes!!!

Peel potatoes. Cut in half, slice the halves into 1 inch cuts. Put in a pot of salted water and boil (about 20 mins--test with a fork until tender).
Drain water...let it steam off a bit.
Add butter and start mashing with a fork...add cream or milk, and more butter as you go until you get 'mashed potatoes'.
Don't forget to add some salt after they've cooked and taste while making adding more salt if needed.
(A touch of garlic powder is nice also and easy).