Now are you talking computer monitors? or TV's/etc?
Computer monitors have been capable of displaying HD resolutions since the early 90's. Only thing some lack is widescreen. Also most monitor's only take VGA inputs, which are normally only from computers.
Dell's widescreens are good examples of what you might consider 'HD monitors' They take multiple inputs, and can nativly display HD resolutions. You can connect and xBox 360 straight to it.