MK-
Cosmic Ray's. Reasonable variety and a good fixin's bar, plus high quality intergalactic entertainment from Sunny Eclipse. Who could ask for more?
Pecos Bill's also has a good fixin's bar, along with more western themed food in a nicely themed setting.
Epcot-
La Cantina de San Angel - Pretty good quick mexican food with a nice area to sit by the lake.
Yakitori House - Decent beef/chicken skewers and such with some nice gardens nearby.
MGM-
Sunset Market Ranch- Lots of different stands providing bugers, pizza, etc. Lots of outdoor seating, though no indoor seating.
Toy Story Pizza Planet- Pizza is nothing special, but I like to sit outside and peoplewatch in the Muppet Plaza, listening to Muppet songs.
Animal Kingdom-
Flame Tree BBQ- Pretty good BBQ. Grab a table down by the water.
Tusker House- I didn't care for it, but a lot of people do recommend it.