It depends on your budget, and the prices where you live. There are other things too, like are you planning on overclocking anything? Will you be upgrading it later? Are you building it yourself? Do you need peripherals too (monitor, keyboard, mouse, etc.)?
For the processor I'd say go for an Intel Q6600, in price for performance it can't be beat right now, not to mention it's quad core. But I agree with draggy, I'm waiting to see what AMD's next processors can do (those Phenom's look pretty sweet). But there may be shortages on AMD's newer processors until 2008, and I might just wait for the AM3 socket.
For RAM I'd get at least 2GB maybe 4GB. If you want 4GB though then you'll have to get a 64bit OS. I'd go with the OCZ XTC PC2-6400 2GB Platinum Rev. 2 myself, but the Mushkin, Crucial, or Corsair kits are just as good. If you are going to do alot of overclocking though then a PC2-8000 or PC2-8500 kit might be better depending on the price.
I wouldn't bother with a 250Gb hard drive, right now the best $/GB ratios are with Seagate's and Western Digital's 320GB or 500GB drives.
A good video card for the price is the EVGA E-GEFORCE 8800GTS 576MHz 320MB 1.7GHz. If you are willing to part with a little more cash for more memory then there is the 640MB version, or for a bit less than that a 512MB 2900XT. For a little more than those you can get one of Diamond's Radeon HD 2900XT 1GB variants, but a 8800GTX isn't too much more and would be better. If your still looking to spend more you could look at a 8800 Ultra, but that won't beat a 8800GTX by alot, so they really aren't worth the price.
For the OS I would normally say get Windows XP, because Vista blows and it probably won't be worth it for a long time. But if you want DirectX 10 gaming you will need Vista, and XP can be hard to find if there aren't good stores around.
For the motherboard it depends on what processor you would get and whether or not you want to be able to have Crossfire or SLI. Some decent socket LGA775 (Intel) motherboards are the ASUS P5KC or the Gigabyte GA-P35C-DSR3, those are more budget or mid-range boards though, so if you want high-end you'd have to look at some others. I haven't really kept up with socket AM2 (AMD) motherboards, so I can't offer alot of information on them, but ASUS, DFI, or Gigabyte normally have a good selection.
If you want to get a sound card then the best one right now is the Auzentech Prelude. However if you don't want to spend too much there is the Creative Sound Blaster X-FI Xtreme Gamer. Since you said you will probably wait, then Creative's next series might not be too far off, and I'm interested to see what the shift from EAX to OpenAL will be like.
The power supply depends on the rest of your system, and despite what some people think it's not all about wattage. I don't know too much about them, but if you go
here you can find a bunch of reviews (scroll down to see more). I visit those forums fairly frequently and the guy who made that post knows tons about power supplies.
The case is mostly about personal preference, and how big you want (or need).
All of that info is based on the prices here in Canada, I don't know if they are similar in the Philippines or if they are completely different. Also availability may be different for some of those products. If you are waiting though then I would suggest not picking anything until you are actually ready to buy, because prices change frequently for computer stuff, and newer "better" products are always being released.