If shopping for an lcd monitor, I'd probably pay more attention to the native resolution than to the screen size. Resolution is detail, and it is nice for watching HD video. A lot of HD video is 720p (up to 1280x720 progressive), or 1080p or 1080i (up to 1920x1080 progressive or interlaced). My laptop has a native resolution of 1440x900, which allows 720p video to be displayed completely or stretched to full screen. However, 1080p or 1080i must be shrunk to fit on my screen.
Video frame rates can be up to 60 fps for 720p and up to 30 fps for 1080p or 1080i. (1080i can do 60 half frames per second.)
I guess both the graphics adapter and the monitor would need to support the desired resolution. In the case of a laptop, they are both built in, so it shouldn't be an issue.
LCD monitors can be glossy or matte. Glossy should give you a sharper picture, but is more prone to glare.
My Dell Inspiron E1405 uses Intel Mobile 945GM Express Chipset Family, and has a glossy monitor. I just measured it, and it seems to be about 36cm, just over 14 inches. It is 1440x900, 60hz. Indoors, it is sufficiently bright, but is subject to glare if there are light sources behind me. Outdoors during the day, it seems a bit dim. (Newer laptops tend to be significantly brighter.) I am quite satisfied with the sharpness and image quality, although I wouldn't mind being able to watch 1080p without having to shrink it. Text seems very sharp at native resolution.
Note that anti-aliasing works against sharpness, it makes things fuzzy.
If you want a large size, I might suggest a projector instead of a monitor. I have never owned a projector, though.
If you're shopping for a graphics adapter, there are other considerations if you are a serious gamer, such as hardware 3D acceleration. I think some graphics adapters have hardware acceleration for video also/instead, but I'm not very familiar with the subject.
This message has been edited by MCalkins on Jan 13, 2012 9:19 PM This message has been edited by MCalkins on Jan 13, 2012 9:19 PM This message has been edited by MCalkins on Jan 13, 2012 9:17 PM