PSU
When choosing a PSU, don't stare blindly at the Watts.
Find out how many amps it can deliver on each rail, especially if you are going for top notch GPU's in SLI.
Get a high efficiency model. (the higher the efficiency, the less power will be lost on heat, and the cleaner the signal is.)
There are many excellent hardware geek sites out there where you can research the ins and outs of PSU's, so I won't go into further detail.
PSU is very important link in the chain. Bad PSU, means failing hardware.
Mainboard
Asus or Gigabyte without any doubt.
That's my personal preference based on building PC's for 15 yrs.
Regretted every single time I wandered of that path.
[HDD]
Personal preference Samsung: stable, quiet, fast, longest mtbf in the market.
Seagate's new models are good, WD is back from very bad yrs.
Stay away from all Maxtor and latest Hitachi models.
[Case]
Agree with PParks1.
Antec. Extremely good cases with eye for details and cooling, and decently priced.
Make sure you chose a case with plenty of room and holes for 12cm fans.
Antec's "Nine Hundred" and "Twelve Hundred" are brilliant cases with lots of room, and lots of fan mounts.
[fans]
Silent fans. you can't have enough of them. 12cm. lots of flow, little noise.
Airflow alone isn't worth much if that air is warm.
Blowing cool air in and blowing warm air out as fast as possible is your goal, so make sure that your case has at least 2 x 12cm entrance and 2 x 12cm exit holes.
Get yourself a descent hardware fan controller.
Better than fiddling around with speedfan software.
[CPU]
Well, at this moment I would say intel.
One word of advise. don't go for the over priced extreme versions.
There are plenty of models that with just a little overclocking have the same specs for half the price.
Don't go for maximum overclocking, it will eventually lead to early death, and you will stress all the other components to their max.
Quad core isn't the only option.
A high powered dual core can do the job easily and will save you a lot of bucks on purchase and energy bill.
[CPU cooler]
Quite a complex matter on it's own.
Personally I am not too fond of water cooling, because it doesn't cool the capacitors around the CPU socket.
There are some water cooling systems that do the job, but they cost a small fortune.
Again, do your research with google. There are more sites dedicated on CPU cooler statistics than there are Win7 forums.
[RAM}
Personal preference is Kingston or Corsair.
Stay away from Buffalo. It's crap.
Pay attention to CAS and Timings.
Again, do your research on dedicated sites.
[Graphics]
Can't advise you there since I am not much into gaming.
I'll leave that to the pro's on that subject.
Only thing I can say is that look for models with big cooling bodies and big fans.
Small fans make irritating high pitched noise, and you want to hear the game, not the fans
Some random advise:
Do extensive research on dedicated hardware sites.
Every separate part has it's own dedicated sites.
Will all due respect for my fellow forum members, we don't have the statistics and research data available here that some dedicated hardware site do.
Look for balance. The chain is as strong as it's weakest link.
If you spend the bulk of your money on a Quadcore extreme you will have to compromise too much on the other parts.
Make Excel sheets where you save and compare all the properties of the gear.
That way you'll keep oversight.
Lastly. take your time, don't rush into it.
You'll have to live with the decisions you make for maybe five years, so make them well.
Oh, don't forget the keyboard, the mouse, maybe joystick, the LCD screen.
Good luck
$1500 to spend on a new computer,
I envy you .
. It works out for my HD config, and lets me hang many stealth fans 
