I've got three 19" DELL monitors on my desktop. I have a GeForce MX440 Dual monitor AGP card and GeForce MX440 PCI card. It works pretty well and gives me a seamless desktop acoss three monitors. Best of all, you can put this together for under $100 assuming you already own three nice monitors.
I have my "Start" menu in the center monitor, my icons on the left monitor.
I could have gone to four monitors for about the same price, but the dual VGA PCI MX440 cards can be difficult to buy since so few were made (as opposed to dual VGA AGP).