At this point my dream development PC is anything that doesn't have the company mandated McAfee virus scanner and LANDesk spyware/inventory management software. Although it would be nice to have the fastest harddrives, quickest processors, and most capacious memory, there are other things that prevent it from being useful. It's a shame that my relatively new "workstation-class" computer at work with 8 cores and 12GB RAM feels more sluggish than my three year old dual core PC at home.
I feel like an Apple (be it a Mac Pro or MBP) is sort of a given in terms of "spare no cost development machine" as it's the only option you have to ensure your "dream development machine" will support the platform you want to develop for during the rest of it's life.