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My rationale?
The case is one I have had, cheap but decent. If you take the time you can work wonders with cable management and it has ample room for fans.
I've used Western Digital drives almost exclusively and have had no problems but for one I damaged myself. This one has the new 6 GBps interface.
The motherboard is a bit future proof and will function with upcoming AMD cpus. I'll mention the CPU here as well. Now it is not a quad core but this should more than suffice for the needs you mentioned and if you are going to upgrade in (near) future to the new AMD chips you may as well not go for the most expensive CPU now.
Graphics card is from what I gather about as powerful as the HD 5850 which I use presently. I am yet to find need for a more powerful card. I game at 1980x1080.
The power supply. I would go for this simply because it had 675+ ratings on newegg with an average of 4 eggs. It is modular for better cable management.
Four gigs of ram and Windows 7 64 work nicely.
That's about it but I will tell you there is a lot more choice out there even if you have a small budget.