Best Graphics Cards For The Money: February 2011
will give you recommendation for several different price ranges and also mention what type of gaming experience that card would give you on different resolution monitors.
Radeon HD 4650 Great 1280x1024 performance in most games, 1680x1050 with lowered detail
Radeon HD 5670 Exceptional 1680x1050 performance in most games, 1920x1200 in most games with lowered detail
and so on.
The Radeon HD 5670 would give you that Exceptional performance on your 1440x900 monitor.
You could pick one up for around $65 after rebate: ttp://www.newegg.com/Product/Product.aspx?Item=N82E16814121410
And it would require an 'average' 400W PSU or a very good 350W PSU.