Need I say more. Easily obtainable at local Office Depot. Freestanding and clamp mount spring arms. Comments Seemingly a recent entry into the office accessory foray. Basically, Kensington created a line of doc holders like everybody else's.
Advantage is probably low price and readily available at local office depot.
Luxo Corp. 36 Midland Ave. Solid steel and built like a tank. Has a dual pivot arm that clamps to desk edge. You would use this to hold a newspaper page, a large blueprint, or some sort of industrial application. I know of no other product like this.