I was actually just customizing a new system (but decided I didn't want to drop $500). Here's what I would recommend now:
PROCESSOR: $180
AMD Phenom II X6 1055T Thuban 2.8GHz 6 x 512KB L2 Cache 6MB L3 Cache Socket AM3 125W Six-Core Desktop Processor HDT55TFBGRBOX:
http://www.newegg.com/Product/Product.aspx?Item=N82E16819103851Why: Top of the line 6-core processor for an amazing price (compared to i7's from Intel) not to mention, only 95W vs 125W for the 3.0Ghz version that is exactly the same otherwise! Also is a retail box so it includes the heatsink/fan (you could upgrade if you want, but no point if you're trying to keep the budget down, plus it's 30W lighter in the power department)
MOTHERBOARD: $103
ASUS M4A88TD-V EVO/USB3 AM3 AMD 880G HDMI SATA 6Gb/s USB 3.0 ATX AMD Motherboard
http://www.newegg.com/Product/Product.aspx?Item=N82E16813131646Why: First, USB3.0 (2 ports). Might as well get it if you're building a new PC now. 6Gb/s SATA ports (5 of them). HDMI, Digital-Optical, etc. are nice bonuses!
MEMORY: $120
CORSAIR XMS3 8GB (2 x 4GB) 240-Pin DDR3 SDRAM DDR3 1333 Desktop Memory Model CMX8GX3M2A1333C9
http://www.newegg.com/Product/Product.aspx?Item=N82E16820145315Why: 2x4GB gives you room to expand in the future. (Just buy 2 more sticks instead of having to replace all 4x2GB). Corsair XMS is extremely reliable. Lifetime warranty (very easy to deal with)
I'd have to do a little more research on Graphics Cards etc. for the rest of the build, but $403 for the main 3 components is pretty darn nice! I'd probably consider an ATI card simply because the motherboard has a built in 4250 graphics chip that you can do Hybrid SLI (might as well get something out of it, right?). Although, the nVIDIA GTX 4?0 series is not that expensive for a nearly top-of-the-line card! Maybe someone who has research recently could shine some light on the graphics cards! Power supplies/cases really don't change that much so just about anything decent will do (700+W modular power supply, any half-decent case)