TexAAs,
DFW has an observation area on the Southeast side of the airport off of South Airfield Drive. I believe it's called Founders Plaza (or Park). In addition to the close proxity of the runway, there is piped in ATC if you walk up to the monument. The only problem with the area is that it is far more interesting when there is a northern wind since planes will be landing from the south right in front of you. Of course, most days in which there is a northern wind it's COLD outside.