Why not cook real food, put it in a container, take it to work and nuke it? Then you can concoct anything you want - chicken, veggies, etc. You'll feel like you're eating more for the calories than you will eating frozen prepared dinners, plus it won't be full of all the chemical junk those are.
What Ring Girl said. Cook up a bunch of healthy food on Sunday, freeze in gladware or whatever, then you have nutritious microwave dinners for the week.
Discussion of non frozen foods aside....Kashi makes a line of frozen entrees that I think are very good and very nutritious. Most are around 300 calories, 15+ grams of protein, plus fiber. Check em out.
In addition to Lean Cuisine (I agree the panini's rock, also the pizzas are pretty good), my favorites ar the Weight Watcher SmartOnes, and Healthy Choice makes some good ones too.