The Opening of the Key Spread
I use a modified shortened version of it. Takes anywhere from a few minutes to a few hours to do. It is actually the only spread that I work with (though like I say, I don't necessarily do the full Golden Dawn version).
It is totally different from any other spread in that a cards location doesn't perscribe it's meaning. In other words, there is not a card location for "the future" or "the situation" or anything like that. Also, there isn't a set number of cards that you use. In essence, you use the whole deck, but you only use about a quarter of it at any one time. This "quarter" of the deck is cut out by hand, so in reality it can be anywhere from around 15 cards to around 30 cards.
"Tarot and the Magus" is a good book that covers this spread. I won't be able to do it fully here.
-tb