Midtown East pre-fixe lunches?
Pampano, on 49th, b/t 2nd & 3rd, serves modern Mexican cuisine with an emphasis on fish. There is a 3-course lunch prix-fixe for $25. While I haven't had lunch there, I have had dinner, and the food is delicious. Good service and pleasing ambiance as well.
http://www.modernmexican.com/pampano/menu.lunch.htm (Scroll down for the $25 menu.)
Montparnasse, the French bistro, on 51st, b/t 2nd & 3rd, offers a 3-course "Business Lunch" for $19.95. It's been ages since we've eaten there, but I haven't heard anything that indicates the food has gone downhill.