Tom's Hardware is an excellent site for computer hardware as MedNez suggested.
Recommendations for PC spec lines will differ depending on who you ask. Plus, for an absolute "killer" system, you'll be looking at expending well over $3,000, possibly more depending on your peripherals set. It's probably better value to get a system at around $2,000 - $2,500 dollars because it gets progressively harder and harder to tell between mid and upper end systems (apart from the impact on your pocket). Plus, games will only look better up to a point - then a better system just displays it faster rather than better. If you do want a top of the line system, though, look out for:
- AMD Athlon-64 Processor (FX-55 and up)
- At least 1 GB of RAM
- DVD+/-RW Drive
- At least 120 GB hard drive with SATA and an 8 MB cache
- nVidia GeForce 6800 graphics card with 256 MB graphics memory (if you want to play Doom III, stick with nVidia - Doom III was optimised for the GeForce chip and runs worse on ATi systems)
- Sound card, mouse, keyboard, etc.
- The biggest screen you can afford after all that, as well as Gigabit LAN if you want to play multiplayer.
I think that DDR2 is a little overrated at the moment. DDR2 is slower than DDR for the time being because of its higher latencies - as time goes by and it scales up, it'll start outpacing DDR1, but for now, DDR1 is still faster (and less expensive). SLI's also probably a bit of a waste - twice as many components to break, twice the power usage, more expense all round on graphics and motherboard. nVidia's next generation chip (GeForce 7800) will be out in a few months too, and it's expected to smash the performance benchmarks (as will the next ATi chip etc.). Basically, go for what you can afford - it's your system. Have fun!
I_F