So Yme, what kind of trading do ya do? Roll with it baby. If you don't let a little grief roll off your back the mkts will hand you your ass in a hat. Please, do tell.
There are basically 2 types of trading rigs. 1. "The usual"... were RAM does most of the work. (Trading programs and other multi-tasking are loaded into RAM and almost everything is done from there.) In this case, any modern computer with enough PCIE slots to run the monitors you want will be plenty. Any Core2 Duo or better CPU on an appropriate mobo. 2. "Data crunching power"... If your data manipulation runs this route, including having many tic charts open or proprietary/custom indicators which heavily involve the CPU, then you want all the horsepower you can afford... like an i7-960 or proper Xeon CPU on an X58/Xeon mobo...or the new i7-2xxx on an x67 mobo. (Personally, I'd be cautious about the newest chipsets... would give them more time to work out any bugs. X58 and Xeon, on the other hand, are probably safe bets. Plenty of power and have been around long enough that any problems should have been addressed.) I know this still hasn't answered your question, but you haven't yet said whether you need a "daily driver" or a "race car".
Hey Yme, the best thing I have found is building, but if you want to buy one than this is what I do. Windows puts so much junk on computers now. They sound like it will be fast, but the new operating systems take up over a gig of memory just to run. So any computer you buy should have at least 3 gigs ram. Anyway, what I do is dump everything and install windows XP. It is such a fast platform when your running it on a new computer. GOOD LUCK OUT THERE!!!!