Go to
www.CaneCreek.com and look under their shocks section.
I've been using their shocks since about '98, and I've this to say: they're affordable, reliable, adjustable, lightweight, and easy to service at home with no special tools. Their customer service is top notch. They're air damped, which isn't the most sophisticated damping medium in the world, but what they lack in a certain fluidity and consistancy, they make up for in simplicity.
Of course there are tons of other options out there, and you could go whole-hog with an advanced platform valving system on the current Fox, Manitou, Progressive, etc. shocks.
Rest assured that pretty much *anything* you mount to your Joshua will be a notable improvement over the stock Deluxe.