I can always recommend heading over to Newegg.com and putting together a wish list. You can just buy the parts over the course of a year, putting them together as you go whenever you have the money. One of the nice things about having a built PC is that you can just upgrade pieces for bits of money at a time rather than shelling out a few thousand all at once, then shelling it out again a few years later to upgrade.
If you do, I recommend getting the latest and greatest motherboard, if anything. There's nothing worse than getting a top-of-the-line PC built on an outgoing motherboard and then, when they stop making processors for its CPU socket, you need to replace the motherboard and the processor in one go. My wife did that, unfortunately, building a computer with a very nice setup but on a relatively old system. Now, to upgrade, we need to upgrade her motherboard to accept a more powerful processor socket, a new processor to fit that socket, and she needs to upgrade from DDR2 to DDR3 RAM sockets. That's a healthy chunk of change.
The rest you can buy at bargain and then upgrade as you get the money. If you've got an older PC hanging around, it is easier to upgrade that as you go. I've essentially been upgrading the "same" PC for over fifteen years, though its been through at least three rounds of completely replaced parts since I started.