I was thinking of building a new comp soon as well. From the looks of it your going to spend a nice amount of money. And you mentioned you were going to want this to last a few years.
I would wait for the new intel procs to come out the end of this yr, beginning of next yr(i think). I think its the nehalem. From what I have read its an amazing processor. It has the memory controller on the die, so no need for the northbridge chipset. Also uses DDR3. Runs cooler and uses less power. If you really want a killer system to get you through a few yrs I would wait a little bit.
Just my opinion though