Best graphics card for playing on 50" tv

My current pc

Asus p5b deluxe
C2DUO E6400 @ 2.13
2gb Corsair ram
74 GB Raptor - OS
74 GB Raptor - programs
Antec 550w psu
Asus 9800 GTX GPU
xp sp 2
Monitor - dell 2007wfp - native 1680 x 1050
TV: Sony KDSR50XBR1 - 50" Wega

I use the pc as my main machine, and sometimes to watch movies on my tv. My tv is connected via a dvi to hdmi cable. I can run windows at 1080 resolution fine however i drop it down to 720p so I can read from across the room.


I am looking to play games like

star trek online
ms flight simulator X
call of duty
star trek legacy
counterstrike
Fear
any other pc games

I currently can run most games at or around 12x10 resolution with full settings without any issue, FSX can sometimes given a little lag. I can push it up to the monitor native resolution also, but have to drop some settings.
On the tv, i have only experimented with game resolution of 12x10, some games look like they stall a little when pushed to 1080 resolution.

Eventually i will build a core i7 system, with win 7 64bit, but im taking it one step at a time. I would like to play games on my tv with the current system at 1080 resolution.

I am thinking about nvidia however i am flexible. Please advise.