The proprietary drivers have worked OK for me, but I've had issues with playing video. I just couldn't get smooth framerates. The radeon driver was worse in that aspect. I swapped in two nvidia cards and video looked much better. It should be fine for general use and I'm still trying to make the ATI setup work. I don't need 3D, just video.
I have a 5870 eyefinity 6 that has 6 display ports, but those are no longer made and expensive (and overkill).
I found a $60 Radeon HD 6450 card made by Sapphire on Newegg (N82E16814102960) that has two dvi and one displayport, that should work for three monitors. There are other options as well of course, just make sure the cards are advertised as supporting eyefinity and they have at least one displayport adapter. I've had success with an Accel active displayport to DVI adapters.
I have a 5870 eyefinity 6 that has 6 display ports, but those are no longer made and expensive (and overkill).
I found a $60 Radeon HD 6450 card made by Sapphire on Newegg (N82E16814102960) that has two dvi and one displayport, that should work for three monitors. There are other options as well of course, just make sure the cards are advertised as supporting eyefinity and they have at least one displayport adapter. I've had success with an Accel active displayport to DVI adapters.