You don't say if you're interested in sit-down lunches, but in case you are...
Montparnasse, on 51st, b/t 2nd & 3rd, is a pleasant French bistro. In addition to the a la carte menu, there is a 3-course lunch prix-fixe for $19.95.
Pampano, on 49th, b/t 2nd & 3rd, serves excellent modern Mexican cuisine. A la carte + a 3-course lunch prixe for $25.
(Note: Nearby is the Pampano Tacqueria. Take-out and delivery only.
Do a search on the Manhattan Board for "Midtown East lunch" and you'll find a ton of suggestions. There are a lot of us in the same boat. That said, there's the Daisy May BBQ Cart on 47th and Park, Zip Burger on 52nd and 2nd, both Quiznos (50 & 3rd) and Chipotle (52nd and Lex) for higher end fast food (beware that Chipotle is constantly mobbed) and you're within walking distance of several good Halal food carts, to name just a few.