Well if possible I do want my organs donated to those who can use them, but I don't think I could ever donate my body to science...that one just doesn't sit well with me....
Personally I would like to be cremated. My mom says she thinks that Roman Catholic's can't have their ashes spread, so I would have to check that one out, but I don't care much about my ashes, either bury them in the cemetary or if church allows it, throw them into the wind at some nice scenic spot....
The only thing I have made really clear to my family though is when I die don't bury me in a dress (assuming no cremation). I won't wear dresses or skirts in life, I don't want to wear them in death either!