I have an ATI 9500 Pro. So far, it runs fine on all sims. At least, it runs as well as my GF2 MX did with the same headaches created by newer versions of DX and Windows XP. I woudl recommend it as the sweet spot for performance versus cost.
SF runs fine, although I do turn off shadows. I have not had to mess with my smartgart settings as other have (EPox 8kha+, AMD 2000XP, 512 mb RAM, Catalyst 3.0a drivers). I suppose my standards can are lower :P
For those who want to mess with their settings, get the newest Cat drivers and install them (be sure to uninstall the old drivers first!). Go to display properties ->Advanced->SmartGart. From there you can disable fastwrites and set your AGP to 0.
The reality is, if you are really into flight sims, you probably do not need the fastest video card on the planet. Due to all the behind the scenes calculations the flights sims are notorioulsy CPU limited. You'd be better getting a so-so card, such as a Radeon 8500, GeForce 3 Ti 500, or GeForce 4200, and spend the extra money on the biggest CPU you can buy.
And for everyone waiting for the new FX card....it will have its share of new hardware bugs, will check in at $400, will probably take up two slots in your case, and may require you to get a new power supply (as many 9700Pro users found out). So don't expect that to be the holy grail of vid cards (especially when the dual channel DDR 9700 Ultra is right behiond it...it never ends :(
So I guess the question is...how much flying do you want to do today and how much do you want to invest for the future?