can't think of any sites off the top of me head.
but look for site reviews about hardware.
like
http://www.tomshardware.com/
that's the only one that comes to my mind.
Memory
memory is cheap, by lots of it. and if you're looking for a quality made product buy
crucial memory , it's microns own outlet store - it's micron ram with tagged with a company name of crucial. (I've got 1.5GB DDR ram and it makes a world of difference.)
Video Card
look for a very good video card either an ATI or nVidia based chipset, all others are useless crap.
I installed an ATI 9800 Pro in a coomputer the other day, it's a nice card, but I hate absolutely hate the driver install for ATI's it's a bitch.
I also just bought a newer nVidia Geforce4 Ti 4600, and I've used them for a long time great cards, easy install nothing more to ask for.
I'd suggest the nVidia GeforceFX (the 5700 model at least, if you can swing the $$ go for the 5900) , if you're looking for quality go with PNY,TYAN,JATON,LEADTEK. for tha manufacturer.
Processor
I'm biased here, but AMD has always kicked ass for me.
Motherboard
again I'm biased but I use TYAN alot, have never had a single problem
Power Supply and Case and Cooling
ANTEC, only way to go, they make kick ass poer supplies. if you don't buy an antec case and supply make sure you get a very good power supply or you'll find yourself needing to replace the cooling fan in the power supply within one year.
I suggest a water cooling system if you don't want the thing to sound liek it's godd grow wings and take off, if noise isn't a problem I can't stress enough that you need reliable cooling for the processor it makes a world of difference.
Hard Disk
Western digital used to be my preffered but I've had to many problems lately.
I lost 2 Hard disk's in my server in one year after buying them (thank someone for DLT backup). I've started using Maxtor, and have had nothing but great things to say about them and if you want to dish out some $$ go IBM.
also disk space is cheap 120GB for like $80 these days.
Have fun building your new friend.