This is mostly a personal requirements and budget issue. Going up the ladder on the 8800s you simply pay more for higher performance. It just depends on how much performance you chose to pay for.
If you have specific usage requirements (e.g. specific games, resolutions, and settings) maybe someone could provide some insight. If so don't forget to include information on your monitor and - unless you are sure it is not an issue - your PSU.
I want to play Starcraft 2, The new need for speed, Counter-strike:source and Fear on full settings. I currently building a rig, so if anyone wants to recommend me a good monitor i would appreciate it.
I'd have to say stay away from the 8800 GTX Ultra unless you want bragging rights and you have deep pockets. At the very extreme top end of the scale you get diminishing returns for your investment.
As for the 8800 GTX from all that I've read, it's a fantastic card, driver issues aside (which affect all 8800's). This is probably the performance pinnacle before getting hosed cost wise, and if you do your shopping well, you may get it for a decent price. The 8800GTS 640 is probably the sweet spot for performance and price. Going lower down the scale, you sacrifice too much performance for the money saved IMO.
As for X2900XT, it competes well with the 8800GTS 640, and even competes with the GTX in some benchmarks. It seems to improve with every new benchmark to. That said, it still has some performance issues when AA is enabled which tends to place it behind the 8800's. I can't look into the future and say that DAAMIT will improve the driver to the point that this argument is moot. Also something should be said by the amount of power this card uses. The X2900XT uses more power than the GTX while the latter performs better in most cases. So you need to decide if running the X2900XT at lower FPS and using more power makes sense to you. Don't get me wrong, I love ATI, just not this round. They really took too long getting this card out and made in my opinion the wrong design decisions. Someone totally loyal to ATI would say otherwise I'm sure, but I am a performance whore, so my dollar goes to the best performer at the time.
I don't know if that helps, but I thought I would give you my two cents worth.
Good monitor choices include Samsung, Viewsonic, LG. Make sure to buy the monitor at a local shop with a good return policy. Some stores will not refund or exchange a monitor with 5 dead pixels for example, and even one of the wrong color in the wrong place can screw up the whole experience.
none of them cause new series coming out soon that support dx 10.1 and those cards don't support it apparently. Therefore, you should wait as before the cards supported the dx updates but apparently now they aren't the same...
Yes, that's the one I'd pick from all the 8800 GTS 320 models at newegg. With the eVGA you can use the step-up program 3 months from now and upgrade to one of the DX 10.1 cards, if you really want.
I wouldn't worry much about DX 10.1 support. That will be available only to 10% or so of people in the next 2 or 3 years, and game makers will make absolutely sure their games work for the other 90% of the market too. They're not suicidal, you know