Need a good graphics card under 2500-2600 for Ubuntu.

Hi, after having a horrible experience with integrated radeon 4250 (everything in Linux is choppy), I want to buy a cheap NVidia card that will run Unity and KDE well with all desktop effects and playing snes games in emulation @ 1440x900 and light gaming with source games like Half-Life 2. My monitor is VGA connected, so I need one with VGA support (hopefully by default). I don't know whether my board supports PCIe x16 or x8 or x4 or x1, but it's a Gigabyte GA-880GM-d2h rev 3.1. Thanks for any advice, I want the best in this price range. Also, I prefer buying online from a reputed site. So any links appreciated,. Please help quickly, I need to buy soon as possible.

MY PC is Amd 970 BE, 3.5Ghz x4 with 4gb ram and corsair psu 450 watt (vs450).