Sites to find great vacation rentals?

VRBO.com - Vacation Rentals By Owner. I'm in the UK and last summer hired a place in the US through them. Dealt directly with the owner, which is always better than some counldn't-care-less agency.

foreign or domestic?

If you are looking for a good beach vacation rental, try http://www.villagerealtyobx.com
We always use them when we go to the Outer Banks of NC.