I want to build a system with 8 CPU cores

I want to build a custom system with 8 or more CPU cores.  Is this possible with any Intel or AMD (or any other "x86-compatible" company) chips?  What about motherboards that support this?

I need to build such a computer that'll take care of intensive rendering sessions for my graphics work, and my desktop computer I use is underpowered for anything other than Preview-quality renders.

Only servers and specialized apps require that sort of power. For you >1, I'd agree with >>2, build a distributed network render system. Your rendering system is a failure if it fails to do distributed rendering.