I am buying a new spa and I have a 4 wire service panel and planned to install a GFCI sub panel outside 5-10 feet away from spa, however my spa only uses 3 wire, 2 hot plus ground. What do I do with the neutral(white) wire, should I just run 2 wire plus ground form the GFCI box to the spa and if no neutral is used by the spa how with the GFI work, I thought those needed the neutral to work correctly. Also is having the GFCI switch sufficient as shut off or should I get a box that has the combination GFCI and pull out breaker in one box, those seem hard to find. Thanks.

I always Reccomend that someone get the GFCI Load-Center with that attached disconnect, I believe most if not all states require a disconnect within 10 feet of the spa and it's a good idea to have one anyways, below is a link to a GFCI that has all that stuff and only requires a neutral be brought to the GFCI itself, after that you can run your 2 hots + ground from the GFCI and it will work great detecting the differential between the two hots and the ground.
http://spapartsnet.com/p_Spa.Parts_TJ0087_744_1_1.html