I was just looking at Newegg and discovered that numerous gaming oriented gpus had gone down significantly in price. This might be something to consider if you are planning a new build or upgrade. Even if you don't buy from Newegg, the slash in prices could be more widespread so it is probably worth a look.
I will just list the prices and links here, you guys can decide on the best deals for you're upgrade or build:
(prices include mail-in rebates)
First up is the ATI 4800 series - generally a good value-to-performance choice for gamers:
A single HIS 4830: $90
An ASUS 4830: $100
Sapphire 4830: $105
ASUS and Sapphire both have better feedback than the HIS, and OC potential will also be very important at these low prices at in can greatly enhance the card performance
This means that a 4830 CF costs between $180 - 210
From this it appears that 260 GTX SLI can range from $400-470 depending on card choice. The 216 is toted as a much faster card however due to its increase in stream processors. Hard to tell how this would compare to a 4850 CF/X2 or a 4870 CF/X2
Nvidia has slashed its prices on this card from its original +$400 region and the cuts can be seen all across the manufacturing spectrum. However I don't know if it is enough..
BFG 280 GTX: $315
MSI OC 280 GTX: $330
280 GTX SLI from $630 up
Before I started writing this I thought that the price cuts I saw for high-end Nvidea cards had brought them back into competition with the ATI cards. However as I started writing I noticed that ATI prices have also dropped.
For top end performance it will be interesting to see how the drop in 260 and 280 prices will effect the choices in both single and multi-card configurations.
Multi-card solutions look really cheap now with 4830 CF under $200 and 4850 CF at $260, Nvidea doesn't seem to be able to compete with these prices. However they might offer more stable OC and better performance for you, I can't say for certain.
I can however say that the most important things to consider for a gaming pc in my opinion are the type of games that you play and most importantly the screen that you play them on.
For large (30 inch+) screens with high native resolutions you might want to look at CF/SLI solutions and more larger memory.
For example: 4850 X2 or 4870 X2 might be better choices than 4850 CF or 4870 CF due to memory
For smaller screens the GPU processing speed might be more the determining factor:
Then you could for example be better off with either one fast card like an OCed 4870, 260 or 280;
Or a less memory oriented 4830, 4850 or 4870 CF solution.
However I'm not certain of this in all cases, so it is always to do some research.
You might have missed it, but AMD dropped the price of the 4870 down to $199 a few days ago. Everything else got shifted probably due to this. These prices should be in effect after christmas as well. (check Hard for the article, I think I read it there.)