OK Seeds, this is going to be a bit of a novel, so bear with me...
There are no golden rules for things like linkage, shock placement, etc. A lot of companies doing different things, and a lot of those are good bikes. What is more important is the intended usage, as that can drive towards a particular bike with specific ride characteristics. First of all, we understand that you won't be doing much pedalling, if any. Therefore, I will hereafter only discuss the really "big bike" segment...bikes with lots of travel, many of them set up with dual crown forks etc, but not very good for pedalling (just know that today, there are bikes that can handle waaaay more DH/FR-type abuse than back in the day, and still pedal almost like a XC-bike from back then as well).
I would say for simplicity that you need to divide up between FR frames and DH frames here. FR frames are typically a little bit steeper in the headangle (around 66 degrees), a little bit shorter in the wheelbase and TT, and maybe taller in the BB. All this makes a bike which is relatively easier to manouver around, will typically "pop" more off jumps, but will compromise on stability. The pure DH bikes are longer, lower, and slacker (64-65 degrees HA), will tend to "hug the ground" more, and are generally built for maximum speed (as opposed to "flickability" or general "fun" factor). I am not saying DH bikes are not fun, nor am I saying they can't be jumped - I am just trying to paint a picture of how these 2 main types of big bikes differ in behavior. Lots of people will now chime in and say how they kill it on their jumps with their V10s...that is not the point.
You mentioned "hucking off some ledges"...which would tend to lean towards the FR side of things (just to check: you don't see yourself trying to squeeze a few seconds out of each run, going as fast as you can over really gnarly and rocky terrain for example?).
Examples of frames in the FR category: Santa Cruz VP Free, Intense Uzzi, Giant Glory (FR version), Morewood Zuza, Trek Session FR, Specialized Demo 7 (or on the "lighter" end of the FR scale, some of which can also be pedalled around a bit, Specialized SX trail, Trek Scratch, Commencal Supreme, Intense SS). OK, that should give you an idea.
DH frames: Santa Cruz V10, Intense 951 or M3, Trek Session DH, Specialized Demo 8, Giant Glory DH (both old and new version), Commencal Supreme DH, Morewood Makulu, Rocky Mountain flatline, Transition TR450 (new and SEXXXXXY!!).
There are also a lot of "boutique" manufuacturers to check out if you want to go non-mainstream...frames like the Evil Revolt, Canfield Brothers have several frames that will do either or, Banshee, Cove, etc etc.....the list can be made endless!!!
Typically, Alu frames are where it's at. You won't find much of anything else.
Linkage types...there is no one "right" answer. Virtual pivots, single pivots, single pivots with linkage...they all have their traits and characteristics, but they have all evolved to a point today where they function very well..not much talk anymore about things like brake jack etc...some designs are more "flexy" than others (oh and there is a bit of a standing joke around "flexy"...you'll pick it up if you hang around...
), but most designs are fundamentally sound today.
Dual crown forks: Boxxer 2010 (Race or Team), Fox 40 (expensive!), Marzocchi 888 if they have their **** together for 2010 (avoid 2008-2009!).
For FR, you can also go with a big single crown fork...either a RockShocks Totem or a Zocchi 66 (again, only pre 2008 or 2010) would be the most prevalent choices.
For brakes, you managed to dig up the spec list of a bike running the worse brakes in the world. Never buy a bike with old Hayes brakes. Stick with Avid Code, Shimano Saint, or newer Hayes (Stroker 2009/2010 for example). Tried and true.
For the rest..you know...whatever..deraileurs and such...SRAM or Shimano...pick your poison. SRAM have made huge inroads in the deraileur market (with good reason if you ask me...).
Don't buy a $500 bike, even used. There are no miracles in the world anymore (all the miracles disappeared as humanity "progressed"). If you want a good used bike that will allow you to enjoy progressing with the sport again, look to spend $2 to $2.5k, for something that is a year old or so. $1500 can be OK too (there are deals to be had these days with luck!)..but it gets harder to get lucky in that price range.
OK, I hope to have been of some use. Feel free to ask follow up questions, but try to get a bit more specific (maybe post up some examples of frames/bikes you are looking at for opinion etc).
Good luck, and welcome back!