Just a few touch-ups aside from the discussion going on here already, and I do apologize if it has already been addressed here but I'm too lazy to read tall these posts.
Old WD Raptor vs New Raptor X
These are two different drives, and the newer one is better. As of this date it is pretty much the fastest SATA drive on the market, in all categories. The old raptor did actually have a slower sustained transfer rate than some of the newer 7200 RPM SATA drives which support SATA 3.0 and NCQ. Noise levels with the 10K Raptor X are minimal...to put it in perspective, this drive is much quieter than the 7200 Maxtor MaxLine III which was actually touted as a decent drive. Its an "OK" drive, I didn't care for it much. The Samsung SpinPoint drives are an overlooked contender for speed and very quiet drives, but like most things korean, quality is still unchartered territory so make sure you back up if you opt for these.
OnBoard Sound vs Quality Sound Card
No "ultimate" pc would be caught dead settling for onboard sound. You do realize that onboard sound is essentially emulated in software...there is no real DSP chip to process special effects or 3D sound like most games these days have. I'll recommend a creative Audigy 2. The X-Fi cards look nice on paper, but read up on compatibility issues. You may also want to consider an external solution that plugs in by USB.
Reliability of Motherboards
Each MB manufacturer produces "gold" and "crap"...you really can blanket one manufacturer as consistently producing crap, unless you're talking about SiS from the old days. Oh, and anything based on a VIA chipset would be "crap eligible", but it's really a toss up if you will have random WTF problems or not. Nforce or Intel chipsets are well-suited for speed and stability. If you want reliable overclocking, shell out the extra cash for a MB designed for that purpose.
Cases
I've built several PCs using CoolerMaster cases, and I can't say anything bad about them. For the money you spend, you get excellent bang for the buck. I personally use the original CM Stacker, which is absolutely awesome. The included 120mm fans ARE VERY QUIET and flow plenty of air. You do not need to go crazy with fans like some people do. 120mm in the front at the bottom and an 120mm exhaust in the rear is plenty. My internal case temp rarely exceeds 1-2 degrees C over ambient room temp.
Budget
Maybe you did, but I didn't see you say anything about a budget for this PC. It would probably be helpful if we knew what kind of cash you are willing to dish out.