Well, let me start by saying that Amarillo is about the least food friendly town that I have been to in a long time. That said, my vegetarian wife and daughter were able to find some pretty good eats there and I thought that I would share since there is almost nothing posted about Amarillo on this website.
Lunch @ El Bracero II Mexican
Very good salsa/pico, good standard mexican fare, more authentic than many tex mex places that might as well be ChiChis or just another blah chain. Very good mushroom, spinach enchiladas that were vegetarian, no vegetarian beans---but they were good. Very good ceviche(fish/shrimp) tostada for under $3. Cheap.
Dinner @ Kabuki Japanese Grill/Sushi
Suprisingly good and fun atmosphere. This is not a gourmet destination, but everyone is very nice there, the food is good enough and they made it a very fun destinatation for us with our 10 month old who loved watching the tableside cooking. Atmosphere is a bit over the top---see website---but rain show, waterfall, ship are all fun. The sushi/sashimi was surprisingly good given the location. Again, don't compare to the big cities, but not bad at all and tasted fresh.
Lunch @ Pepito's Mexican in Canyon, TX near Palo Duro Canyon was a good enough standard fare Mexican place. Very good fish tacos special, otherwise, the service was good enough and food was fine.
Breakfast @ Main St. Bakery Grapevine, TX(near DFW)
Nice bakery with very good food. If you have a couple hours or more at the Dallas Fort Worth Airport, this is a 10min cab ride and a nice place to grab a bite and hang out in a cute little town. A pleasant surprise.