VIVO Triple Monitor Desk Stand
This screen desk stand out of VIVO is the only one with this list that has a base that sits on top of your desk, rather than clamping on the border. This is the best option out there, if this is what you are looking for.
This model supports a maximum screen size of 30-inches, so if you have anything over that, be certain you buy something a little more beefy. The aluminum and steel design makes for an extremely sturdy stand, making sure that the tracks are not going to get ruined by a stand failure.