Second Graphics Card for a Third Monitor

I currently have Dual Monitor setup on my (Zotac) GeForce GTX 460 with two Samsung SyncMaster B2030 (20") Monitors.
I would like to add another graphics card to set up a third monitor with a Benq 24" LED - GL2450HM.

Specs:
Intel Core i3 540
Gigabyte GA-H55M-D2H (http://www.gigabyte.com/products/product-page.aspx?pid=...)
Transcent 4GBx2 DDR3


My plan is to run the BenQ off the HDMI out on the GTX 460 and get a second Graphics Card to run both the Samsung Monitors (They only have DVI and VGA inputs).

I do not require Crossfire or SLI. I do game quite a bit, my I'm happy with what the GTX 460 puts out. My other main activity is video editing with Avid and Premiere and some other applications that need a decent Graphics Card and also stretch across multiple screens.

I have no clue about whether to go with Nvidia or AMD for the second card. Or whether there would be any compatibility or driver issues with the motherboard or Graphics Card(s). Plus I need the performance to be pretty damn stable.

Would really appreciate suggestions for the second card. Preferably something from the below sites. (Not too many options in India). Also, the cheaper the better. Mainly just looking to run the Desktop and Browsers on the 2 Screens and leave all the heavy lifting to the GTX 460.

http://www.flipkart.com/computers/components/graphic-ca...
http://www.theitdepot.com/products-Graphic+Cards_C45.ht...

Thanks

P.S. First time posting. Apologies for any faux pas.