Today nVidia released the GeForce 8500 and 8600 series, providing DirectX 10 graphics cards for the $200 and lower price ranges.  The cards are based on the technology used in nVidia's high end GeForce 8800 series cards, though cut-down for the budget markets.

While you need Windows Vista to run Dx10 and there are currently no Dx10 tests commonly available to determine how well they perform with Dx10 shaders, below are some of the reviews up on the net using popular Dx9 games and benchmarks and comparing them to nVidia's GeForce 7 series and AMD/ATi's Radeon X1k series:

AnandTech

ExtremeTech

Hot Hardware

Elite Bastards

Tom's Hardware

Below are some comments from the above reviews:

The new GeForce 8600 GTS and GeForce 8600 GT cards are a bit of a mixed bag.  On one hand, they offer all of the cutting edge features of the GeForce 8800 series, and then some.  These new cards offer full support for DirectX 10, CSAA, high-quality anisotropic filtering, and they feature an enhanced PureVideo HD engine that puts them a step ahead of even the GeForce 8800.  The GeForce 8600 GTS and GT will also hit the market before any competitive DX10 offereings from ATI, they run relatively cool and quiet, and their power consumption numbers are lower than current mainstream graphics cards. On the other hand, the GeForce 8600 GTS and GT don't perform on the same level as last-generation's GeForce 7950 GT and Radeon X1950 Pro, despite the similar price points currently. We should also note that the $220+ price tags of pre-overclocked GeForce 8600 GTS cards is within striking distance of the significantly more powerful GeForce 8800 GTS 320MB, which could be had for about $250-$279 at the moment. - Hot Hardware

On the whole, we're pretty impressed by the performance of these GeForce 8600 cards. Unfortunately, we don't know if these new mid-range graphics wonders are going to be "enough" for true DX10 content. Simply put, there are no real DX10 games for us to try out. We know there's a DX10 patch coming to Company of Heroes, and Supreme Commander, and quite a few other DX10 games on the way in the coming months. But until they're done, and we can run them in DX10 mode on Windows Vista with all those features turn on that make you say "oh, this is why DX10 is better than DX9," we don't know how well they'll perform. The addition of the new VP2 video processor is exciting, and we'll have more on that in a future article that more comprehensively examines the video quality and performance of various graphics cards. - ExtremeTech

Much as I'm loathe to sit on the fence in the conclusion of such a major review, I have to say that my current judgement on the GeForce 8600 GTS is very much 'wait and see'.  Right now, there are no DirectX 10 titles on store shelves, making the need to upgrade to the latest technology less than urgent - A few months down the line, we'll hopefully see further driver improvements and more intensive DirectX 9 titles to glean performance figures from before the first wave of DirectX 10 games become available, a combination of which will see the GeForce 8600 GTS either sink or swim.  Add in to that inevitability of prices dropping as time goes by on these parts, and I'm really struggling to think of a good reason to pick up a board right here and now.  I really want to like this board for what it brings to the industry and mainstream gaming in terms of both feature set and image quality, but right now it's simply too early to get the necessary grasp on its performance abilities to whole-heartedly recommend it. - Elite Bastards