* Core i7 processor - just the cheap one the 920 I believe, the other ones are WAY too expensive right now
* 12gb triple-channel RAM. Buy two 6gb kits, it's cheaper than a 12gb kit and many mobo's don't support 4gb per slot anyways
* Buy Win7 (releases in October), if you can't wait til then buy a copy of Vista that includes the free upgrade to Win7. Go 64-bit to make use of all your RAM
* GeForce GTX285 or equivalent ATI graphics card or better
* SATA 1TB HDD, maybe buy a smaller 2nd drive to run WOW on a drive separate from the OS.
* ****BUY A GOOD NAME-BRAND HIGH QUALITY POWER SUPPLY!!!*****
* ****BUY A GOOD NAME-BRAND, HIGH PERFORMING AND QUIET AFTERMARKET CPU COOLER!!!*****

Also, go dual-monitor! It's *WAY* easier to 5-box if you have two widescreen LCD's. You run your main WOW on your main screen and divide the other four onto the 2nd monitor into four 800x600 regions (fits nicely on a monitor that does 1680 resolution with just a bit of overlap)