There are head units available, which is integrated LCD panels to display the DVD video and information or cool visualizations for audio playback. Some panels are integrated into the touch sensitive, allowing full control of your player through the video. The panels in May either be fixed and visible at all times, or has motorized slide-out action that allows you to view cached when not in use.
The main advantage of such units are plug and play very well. It is not necessary to spend more time on the panel and the installation thereof. You pay for this ease of installation and lower cost by a (usually) much less than buying a separate screen.
Video-capable head units
These types of head units usually have an integrated DVD player, but the viewing of video on LCD panels is connected to a video output on the back of the unit. These units are less expensive than those that have integrated displays (in particular versions of the touch sensitive screen), but the additional expense of an LCD screen that must be purchased and installed. You can get much more comprehensive than the panels are available in all items in a unit, and to select those that best suited to your budget and viewing preferences. Moreover, these types of headaches can last several screens for the ultimate in awesomeness.
Hybrid Head Unit
These types of head units have both an integrated video on the board may or may not tactile, but also offers external video output. These types of head units are more expensive but offer greater flexibility of installation, the options and control. You can easily add more panels later, using the integrated viewer in the same period. I recommend this type of video on the two heads of others, it is used both in field and for the sustainability of all three options for expanding capacity.
Whatever the type of pick to use, is strongly recommended that you have installed by professionals. Mounting an LCD display in a car and see the good quality, functional and safe work is better for the left to a professional. LCD panels are very easy to ruin, if you care to install them, and once a car is a vibration-prone environment, they must be fitted with safety to prevent possible damage later. And they are not cheap! When it comes to expensive equipment, it is preferable to have an installation done by professionals who can provide security.