As we are all painfully aware, the only way to get multiple monitors AND compositing (Compiz) on Linux is to use a single graphics card that can drive both (or in my case all three) screens.

I bought a Radeon 5750 specifically because it claims to able to drive 3 monitors. I can plug in 3 monitors (2 DVI, 1 HDMI) and the Catalyst Control Center shows all 3, but only 2 can be enabled at a time.

The exact message is:

The current settings cannot be applied.  Possible issues may include:
   - Display(s) cannot be enabled.
   - Setting(s) cannot be applied due to insufficient video memory.

So I'm going to assume that either the 5750 doesn't support 3 monitors, OR, more likely, ATI couldn't be bothered to add that support to their Linux drivers.

So this is a multipart question:

First, can anyone suggest a PCI Express Graphics card that can run 3 screens on linux without tremendous pain? I'm looking for something where you install the driver and all three screens "just work". Does such a card exist?

Second, if you have a 5750, have you been able to get it to do 3 monitors?

I'm running Ubuntu 10.04 at the moment.