WDs and Maxtors are not very reliable from history.
Seagates are among the most reliable but there a little behind(probably because the take time to test their tech).
Also, you may want to think about getting SCSI320 drives+controller for processing and using regular 7200 rpm sata drives.
You may also want to think about raid.
I use 1 SCSI drive specifically just for OSes.
Note: Sata data cables are flimsy and I recommend getting 90 degree cables.
You may want a removable enclosure with sata support.
Sata is hot swappable which means you can plug it in while the computer is on.....just like USB or FireWire.
The opterons are nice(since the xeon dual core is a flop).
You may want to invest in 2 processor because they usually produce better results(especially with dual cores).
You can google dual processor vs dual core and you'll see that dual processors perform better. If your going with 2 single core processors, I recommend xeons.
Also, you may want to wait for the next opteron(which will be released q1 2006) which will support DDR2.
I would choose a turbo cool unit by pc power and cooling.
From the comparisons I've seen they have the most stable and efficient supplys on the market. They specialize in power supplies. They make a wide range of power supply ranging from 310-1100 watts. You probably need something around 400 watts.
There was a comparison between antecs, oczs and other power supplies online.
Heavier usually means better because it means more solid which translates into more stable and reliable power supplies.
I would either choose plextor or pioneer. Pioneer gives you the ability to read and write to dvdram with the new DVR-110\A10. Plextor gives you very high read\write speeds(I'm not sure what that new model is called that can do 18x).
Since your not a gamer, you may want a workstation card from Nvidia, ATI, or even Matrox. That is....if you develop...
Its good to have one, especially when your system dies....some diagnostic apps still use the floppy disk.... USB floppy drives wont due because they usually get assigned a different drive letter. Preinstalled environments for data recovery are mostly on cds but you never know when you will encounter a prog that only want floppy. Zip,klik,jaz,ls, and 5.25floppies came and went but floppies are still used. You may not need a floppy drive if you have another computer using an FDD floppy.
DELL UltraSharp 2005FPW 20.1-inch if you want 2 widescreens.
Or a Samsung or viewsonic
You really should have something ejecting the heat from the case. There should really be a flow of air going through the case.
Depending on how much you have left....a watercooling kit could be an option. No cpu cooler needed...replaced by waterblock. Use fluidXP+ for coolant because its non-conductive. There are many diffent options for watercooling which even include ram shims.
There are slight difference in chemical compositions of these conductors. See the below link to figure out what you need.....
Depending on how you balance you budget you may have to settle for lower brands or parts, but dont skimp out and go for the bottom of the list with no name brands. I learned this the hard way with a 400w power supply that did not have a known manufacturer label.