Sorry it took me so long to reply. I sympathize with you about the Radeon drivers. I recently purchased a GTX 260 instead of a Radeon 4870 for that very reason.
Your computer isn't too terribly old, but any big investments will probably be bottlenecked pretty significantly by your CPU. If you get a new monitor, make sure you factor in your new monitor resolution with the power of your video card (I wouldn't get a 9600GT if you plan on going to a higher resolution).
I don't know how much you know about NVIDIA's card naming system, so I'll explain it real fast to help you find what you want. The first number is the generation series (
9000,
8000,
7000, etc). Higher is newer.
The second number basically tells you it's overall performance. x
8xx is generally the highest performing (9
800GT), x
6xx is generally a good price-performance budget gaming card (9
600GT), and anything lower is going to be quite weak for gaming purposes.
Note that the newer generations do not automatically equate to more performance; a 9600GT is not better than an 8800GT.
For reference, a 9800GT is almost the exact same as an 8800GT, and I was able to max out Team Fortress 2 with everything on the highest settings, 16xAA and 16xAF, at 1680x1050 resolution, with no noticeable slowdowns on my factory overclocked 8800GT. 9800GTX
+ (note the
+) is a faster, more efficient 9800GT.
Also, some noteworthy companies to look into: EVGA (Step-Up program allows you to upgrade to a newer card if you register it within 90 days, where you only pay the difference of price and shipping), BFG (similar program, but I believe it's for 100 days), and XFX (Double Lifetime Warranty - meaning you get a lifetime warranty, and anyone you sell the card to will also have a lifetime warranty, effectively raising its resale value). I don't know much about the other companies, unfortunately.
Here are my recommendations for current sales (this could easily change within a couple days):
For raw power and an excellent deal:
http://www.newegg.com/Product/Product.aspx?Item=N82E16814187052
For good power and a couple free games:
http://www.newegg.com/Product/Product.aspx?Item=N82E16814150316
Also, there are some good GTX 260's can be had for a little over $200.
On a final note, make sure you have adequate space and cooling for a new video card.
Let me know if you have any questions. Also, I apologize for the long read.