Case, it's the most lacking component I see. Get an NZXT Switch 810, you'll love it.
With $130 left, go for a 1TB HDD, or a modular PSU (I recommend SeaSonic) if you haven't already got one.
Other options for the remainder are a better SSD like a Crucial M4, or better cooling like a Noctua DH-14, or some new case fans, I prefer Noctua's NF-F12 PWM.
As much as I hate AMD, I think you'd be wise to stick with your current setup for graphics, unless you hate it or need more. If so, get a Gigabyte WindForce OC 660.
Don't forget about selling your old components, you can upgrade even more after you put in a few new items!
So, my upgrade order for this would be:
1. Modular SeaSonic PSU
2. Switch 810 Case
3. Noctua DH-14 CPU Cooler
4. Crucial M4 128GB SSD
5. Gigabyte WindForce OC Edition GTX 660 Graphics Card
6. Noctua NF-F12 Case Fans