The majority of the 18, including its #1 (which is #2 on the overall list), Fortune 500s in DFW are Energy/Oil (Exxon #1). There's definitely TI and a bunch of Airlines and Healthcare (which I totally forgot about). I'm not putting down Dallas, I just hope it doesn't get really hurt by whats going on in with energy/oil.
Houston is in a pretty scary position right now. When I drive through it, it's absolutely insane how much development they've had over the last 5 years that are Oil/Energy companies that you can see right off the highway.
Maybe you don't consider F500 the market, not sure that I do, but those companies do employ a huge number of people. Austin only has HQs for 2, Dell (44) and Whole Foods (264) but Austin is a very different market. People absolutely loathe large chains here.
2 Exxon Mobil (Irving) *
12 AT&T (Dallas)
112 American Airlines Group (Fort Worth)
124 Fluor Corporation (Irving)
130 Kimberly-Clark (Irving)
143 HollyFrontier (Dallas) *
146 J.C. Penney (Plano)
175 Texas Instruments (Dallas)
203 Dean Foods (Dallas)
205 Southwest Airlines (Dallas)
262 GameStop (Grapevine)
266 Tenet Healthcare (Dallas)
292 Energy Future Holdings (Dallas) *
351 Energy Transfer Equity (Dallas) *
361 Commercial Metals (Irving)
341 Affiliated Computer Services (Dallas)
388 Celanese (Dallas)
404 Dr Pepper Snapple Group (Plano)
473 Atmos Energy (Dallas) *
492 RadioShack (Fort Worth)
493 Wistron (McKinney)
Houston
4 Phillips 66
45 ConocoPhillips
64 Enterprise Products Partners
65 Sysco
77 Plains All American Pipeline
106 Halliburton
135 Baker Hughes
136 Fluor
144 National Oilwell Varco
167 Apache
174 Marathon Oil
200 Waste Management
233 EOG Resources
265 Kinder Morgan
310 Cameron International
334 KBR
343 Group 1 Automotive
344 CenterPoint Energy
381 Enbridge Energy Partners
397 Quanta Services
417 FMC Technologies
435 Targa Resources
451 MRC Global
459 Calpine
475 Spectra Energy
Not known Buckeye Partners
Not known Noble Energy
Not known PVF Resources LLC
edit: Damn, the formatting is terrible. Sorry.