What hub to purchase for a GT aggressor? I have a GT Aggressor 1.0 

Specs here: http://www.gtbicycles.com/2013/bikes/mountain/trail/aggressor-1-0

Recently on a long ride, the crank started to roll freely after a long downhill.  i.e. when pedaling, the cycled does not move because the rear freewheel simply rolled freely without engaging.  I think the problem is with the rear hub which may need to be replaced.

From looking at the specs, the hub is a "Alloy Cassette Disc QR".  Trying to find it at amazon.com, there were so many to chose from and did not know which one to purchase to replace this.

Any advice is much appreciated.

Thanks you!
There are plenty of wheels that will fit that bike, and they may very well be less expensive than having the hub overhauled.

You want to find a 26 inch wheel with an 8/9 speed cassette compatible hub, with 32 spokes ( that's the 32H part )

I actually don't see any on Amazon.com that fit the bill. This is one of those times I would head into the local bike shop to make the wheel replacement process quick and easy.