Pretty much standard is:
flat seat with crush washer = 25lbs/ft
tapered seat no washer = 15lbs/ft
Crush washers are supposed to only be used once. You can still buy them seperate at good old fashioned autoparts stores.
just a touch of antisieze goes a long way to making them come back out nice and easy, and is a requirement when installing plugs into an aluminum head. Be very stingy with the antisieze though as it is insulative.
Very good question! I've seen a lot of people who over tighten spark plugs, oil filters and oil drain plugs.
Scott