Size of monitor for watching movies

I am going to be buying a new screen for my desktop and its going to be bigger than my current screen which is 17 inches. I watch a lot of movies on my desktop so this time I want to get a good sized screen. Please suggest the screen size which I should get, I don't want it to be too big that my eyes start hurting while using the computer or be too small to watch a good movie, so please suggest.

I think a 21 inch monitor would be suffice, it wouldn't b too big for when you want to use the computer or be too small when wanting to watch a movie.
Nothing bigger than a 27 inch screen would be fine. It would be good to watch movies on this sized screen and also if your screen would be placed a bit far away then it would be OK to use it for working on the desktop.