There is many different brands out right now.  Mine is a CM SK body which is a skirted body with toolboxes made into the side of the bed.  I really  like the CM's because they powder coat their beds. 

Pros: easy to hook up your trailer (no trying to jump in the bed), when parking always back in the spot and when the stupid person next to you opens their car door it will hit you bed instead of the door of you truck. no damage to your truck).

A big pro for me: my bed is 9'4" long and I can haul 4 round bales on it!

con: have to be carefull on what you haul on the bed must tie down most items.

If you have a trailer with NO electric or power jack, pay the few extra bucks for the gooseneck trough.  This is so you will not have to raise the trailer as high to hook up.

The cost of mine was 4000.00 but well worth it.  It has 4 large toolboxes, gooseneck trough, lighted headache rack, small side rails, reciever hitch, LED lights and POWDER COATED paint!

I have bought regular flatbeds from J&I out of OK and they are good beds but not powder coated and not as fancy but they are stout.  I have one on another truck and it cost me around 1500.00 installed with gooseneck ball and brake hook up.

I did forget to add the the standard dual rear wheel truck is wider than a C/C model truck like mine so when you buy a bed make sure you tell them you have a regular dually or they will just install whatever bed they have handy and the rear tires of the truck may stick out a little.

I went the aluminum route to get back some payload weight...

http://www.hillsboroindustries.com/Products/AluminumTruckbeds.aspx

Here's the manual...

http://www.hillsboroindustries.com/Support/AluminumTruckBedsManual.pdf

I just had a J&I installed on my 97 Dodge 1 ton "farm truck".  My wife uses this truck for pulling our LQ trailer; and we can get quite a few square bales on the bed ahead of the GN.  The bed cost $1100 (leftover "new" bed); and installation and light hook up was another $650.  I sprayed the entire top surface of the bed with bedliner material to keep rust away longer.  I hope to get my take-off box sold for several hundred, to cheapen the cost. 

I like the flatbed for making the bed area more useable than a pickup box.  As long as you have ratchet straps for securing loads; there is really no downside to them.