I'd recommend getting an i3 and new mobo with some upgraded ram. Usually I'd say to look through the combo deals newegg offers but right now all the i3s come with a micro atx or itx board. Still, you should be able to get all three of these things for less than $300 even with 16 gb of ram.
CPU: i3-3225 GPU: ASUS HD 7850
RAM: 8gb G.skill Disk: 128SSD 2x1TB in raid 0
corsair h80 Power: 500w ASUS p8b75 mobo