The River Cafe is wonderful, Italian, I have only been there once it consistently receives rave reviews, it is however in Fulham so may not be convenient for the West End. Modern British with a spectacular view, you could try The Oxo Tower, 8th floor I think, particularly good at night panoramic views over London, sensational when everything is lit up. Although I would add that whilst the food was okay I think it's the situation that makes it, it does have a buzzing atmosphere inside the restaurant. Locanda Locatelli very good Italian food, but expensive. J Sheekey modern British, fantastic for fish, but they do other things too. I would hasten to add that I don't frequent these type of places on a regular basis, birthdays and the like. Cote's always pretty reasonable for a French meal and reasonably priced and they are everywhere. I have eaten at some good not too expensive French bistros in London in my time, but can't remember their names. Sorry!
Where ever you decide to eat hope you have a great time Teetime 
Cheers!
