What is the best place to store potatoes?

This will answer your question(s):

http://www.cooksillustrated.com/howto/print/detail.asp?docid=1748

I've heard you should not store potatoes near onions.

Oh, and never ever store them on the counter. If you do, they develop solanine, the chemical that causes them to turn green and (in large doses) is not good for humans. Why supermarkets store potatoes in the light is a mystery.

All that cool and dark is correct. However, if it is time to sprout, they will. My potatoes (harvested in September) are sprouting like mad, although they spent the winter in a cold dark cellar. So it depends greatly on when your potatoes were harvested.

Yes, cool dark place. The garage works or the pantry. They get too much light on the counter. And too much temp change.

I usually keep mine on the fridge...but again I'm Brazil and unless it is the midle of winter it's darn hot in here.

Cool, dark place. Don't refrigerate. Usually your cupboard is fine. If you have a recurring problem of sprouting and greenness, you might try using them sooner or buying from a different source. Some grocery stores spray their potatoes to keep them from sprouting, while some don't.