NVDIA GeForce GPU Advice For 64 bit Operation System,please? Urgent

I dont know English well besides my inefficient computer knowledge makes it difficult to select a NVIDIA GPU model.
Please anyone can advise me a NVIDIA SLI Graphic Card which will be suitable for 64 bit operation system.
*If it’s needed names/models of other parts of the pc are:
Intel motherboard: DX58SO (supports SLI graphic cards)
Intel Processor: I7-960 (supports SLI graphic cards)
Kingston RAM: KVRD3N9K3/6GB
Operation Sysytem: PC has 2 harddisks, each harddisk has different operation system. One harddisk has 64 bit Windows7 Ultimate. Other harddisk has 64 bit Ubuntu 10.04 LTS.

*PC will be used in media applications, games etc…
**Ubuntu operation system advices NVIDIA graphic cards, for that reason I should buy a NVDIA model.
***If my topic was started at wrong part of the forum, sorry for that.