i've only ever had stock shocks before so i don't even know where they range from, i am willing to spend for good shocks though because i know it will make the world of difference for my back when i ride. i do mostly trail riding, mud, mouguls. i am on the track maybe one a month.
1. well fox makes arguably one of if not the best shock in the industry. 2. or you could buy some used yfz front shocks and send them to a shock shop to have them set up for your weight and riding style. people say that option 2 is just as good as option 1and is also half the price. im sure others that have after market shocks and shocks built by a site sponsor will chime in and help ya out
First step/stage/level/whatever is a set of OEM YFZ450 or Raptor700 piggyback shocks. They work with stock a-arms and provide a smoother ride with better ability to soak up the bigger hits. These can be found for around 150-300 dollars depending on condition/type/age/etc.
Second would be an entry level aftermarket shock, something like the elka stage 1/2, a works a-t steeler, a fox float, or the like. These are setup for your own application and will perform quite well for a weekend trail ride. These are usually between 400 and 700 dollars.
The next would be a fully adjustable shock, one with all the little dials and knobs on it so you can customize your riding experience. These extra adjustments push the price up to somewhere between 1k and 1500 dollars, but give you the ability to make the same set of shocks perform just as well on multiple types of terrain.
All of those can be run on stock a-arms, but on the 660 you really benefit from widening the machine. A set of +2 or +3 wide a-arms and an extended axle will improve the handling and from my experience make the ride smoother as well. If you're sitting on a couple thousand dollars you can always pickup the 3rd type of shock I listed in "long travel" and pair them with some long travel a-arms with relocated shock mounts. These setups are made even smoother by virtue of larger valving and spring ranges.
I've run everything from yfz shocks to a 2500 dollar Elka/Gibson LT front end on my 660, and while the jump from the stock pogo shocks to anything else is a big one the experience still gets better the more money you spend. This is why jsanders was asking for more information, to better tailor his answer to your needs and budget.