My current PC just effectively "died" over the weekend.
So, I bought a new rig, an Intel 6600 Quad core. I had the local tech at PC Club successfully overclock it to 3.2 GHz, and it runs cool and stable at this speed - though I am going to see how this works out long term. If I have to drop it back down, thats OK, as my goal was 3.0 GHz.
Overall, the cost was not too bad, just over $1000, and thats with 4GB RAM, a 150GB Raptor, and another 500GB drive for data storage. I was also able to salvage my video card (7950 GX2), sound card, and 700W power supply, so this helped kept the cost down. I could have used my older drives too, but since they are all IDE, I figured it was time to purge all legacy crap and get with the program.
I think this could have been done for even cheaper, especially if its for a render-only rig that used older parts otherwise.