Mountain Biking - rear shock advice

So I have a 2005 Giant AC with a rear shock that I'd like to upgrade. Its a stock shock, I think its a Giant HV Coil-over w/125 - 160mm travel, rebound adjustment. I'd like to upgrade to a coil shock that would be good for anything from all-mountain to freeride. What do I need to know in order to get a new rear shock? (My first dually). Any recommendations for a good shock?
I weigh around 190-200 lbs, ride mostly all mountain and am running a 150mm single crown fork

frame looks like this, parts are upgraded:



https://centercycle.securewebsiteserver.net/catalog/images/AC.jpg

You would need to know the shocks eye-to-eye and it's stroke in order to get a new one.

how would I find that?

Easiest way is to call or e-mail Giant.

Take the spring off. Measure the "Eye-to-Eye" distance (mounting hole to mounting hole). Then compress the shock fully w/o spring. Measure the same distance. Take the first measurement minus the last one and that gives you the stroke.

If you're strapped for cash, the Fox Van R is a killer shock for $225 at Universal Cycles. Don't forget to enter the coupon code from the top of the screen to save 10%. It has the factory set Propedal for decent grinding efficiency with a nicely ramping compression stroke. It also has a bottom-out bumper for end-of-travel management. Not to mention the much needed rebound adjustment.

If you're not quite so strapped for cash, the Marzocchi Roco TST would be wonderful for your applications.

If money isn't a concern, check out the Fox DHX 5.0 coil. It's around $400, but infinately adjustable. The Fox DHX Air 5.0 is nice too, but not quite as plush as a coil + you have to worry about pumping it up now and then.

Sure, there are more expensive solutions like the CaneCreek Double Barrel if you're loaded, but who really doesn't like Fox rear shox?

I have a Float R on my dually and I'm going to go to the Van R b/c I hate losing 5psi over a months time. I just wanna lube my chain and roll.

If you do have the cash, I'd still just get the Vanilla R and put the rest of your $$$ toward a nice fork. (unless you've done that already) The fork bears most of the brunt when it comes to sucking up bumps...I'd be more concerned with getting that sorted out first.