Hey there Flyf15:
To be honest, DFW to me is one of the tougher places to spot a wide range of aircraft. If you hang out in one of the terminals, you miss a lot of action. If you ride around in one of the trams, you might get lucky and see something interesting, but you need to be quick on the camera trigger.
DFW has an observation area located on the southeast corner of the airfield, but you need wheels to get there. It's located near the administration building on a small rise. But, there you're at the whim of which ever direction the traffic is going.
If I had some time there, I might try the 2W terminal on the west side, since it has the international carriers, and the oddballs (everything other than AA and DL).
Good luck, let us know how you make out.
Tom in NO (at MSY)
"The criminal ineptitude makes you furious"-Bruce Springsteen, after seeing firsthand the damage from Hurricane Katrina