MK --- Cosmic Rays. Something for everyone from chicken to salads to a vegetarian wrap. Only problem is separate lines depending on what you are ordering. Nice outdoor seating.
Epcot --- We usually do a sit down here. We did have CS at Yakitori House a few times. Although nothing outstanding, the outdoor seating near the koi ponds was quite nice. Healthier food here, so that's a plus.
AK --- Tusker House. Good salmon and vegetarian options. Probably my favorite CS at WDW. Better atmosphere(nice outdoor terraces) at Flame Tree BBQ, however.
MGM --- Have to agree with everyone else, not much here. I have gone to Rosie's All American Cafe for their vegetarian burger. I've noticed a new CS called Herbies Drive-In (on allearsnet.com), and see that they have steamed buns. My daughter loves these, so I'm sure we'll try it the next time we're there.