DW and I went three or four times without kids, and here are some of our favorite sit-down dinner places:
MK - Take the monorail to GF and eat at Narcoossee's, or catch the water taxi to WL and eat at Artist Point
Epcot - In the World Showcase, try Le Cellier (Canada), Teppan Edo (Japan), or Coral Reef in the front of the park. You can also take the water taxi (or walk) to the Boardwalk area and try Yachtsman's Steakhouse at the YC or Flying Fish right on the Boardwalk.
DHS - We really like the Brown Derby
AK - Hop on a bus to the AKL and eat at Jiko
Good luck, and have a great time! The wonderful thing about the sit-down food at Disney is that it is all very good. You can't go wrong!