If I misunderstood and the OP has no rig right now, then Sandy Bridge is definitely the way to go. I just plopped down $1300 including shipping on a pretty high-end Sandy Bridge setup, and could probably shave off $300 to get it at $1000. Of course, I already had a 23" LCD monitor.
My new rig:
Intel Core i5-2500k
Prolimatech Megahalems Rev.B cooler w/ two SilverStone FM123 fans
Gelid GC-Extreme thermal compound
ASRock P67 Pro3 mainboard
G.Skill Ripjaws X 12GB CL9 RAM (one 8GB kit and one 4GB kit)
Palit GTX 570 Sonic 1280MB video card
Samsung Spinpoint F3 1TB SATA hard drive
Samsung SH-S223C SATA DVD burner
Cooler Master HAF 912 case w/ six Scythe S-FLEX SFF21F fans
SeaSonic X-Series SS-560KM 560W power supply
Less CPU, less cooler, less RAM, less video card, and less fans would save more than $300 ... and still be plenty to beat the crap out of an Athlon II X4 rig.