At the MGM we like the 50's PrimeTime Cafe for a sit down meal. You could also consider the restaurants at the Boardwalk and the YC/BC if you have the time. They are a short boat ride, or walk, away. Doing that would take up a fair amount of park time though.
At MK, I too would suggest taking the monorail to either Chef Mickey's at the Contemporary Resort, or 'OHana at the Polynesian. It would be fun to see the Disney resorts as well as eating, and the monorail ride is fun.
As a pp said, check out all of the menus in WDW at allearsnet.com, dining.
This will help you to see where you might like to eat. Always consider the resorts near a theme park as well as the theme park restaurants themselves.
By the way, Welcome to the DIS