First build under $600

So what are you using this build for?

If you plan on gaming, you could go with a phenom ii x4, or an i3.

For your graphics card, go with a 7850 / 7870. Very good cards for the money.

If you wanna sacrifice gaming power, go with an i5-3570k, and for a gpu you could get a 7770.

For the case, go with a Cooler Master 912 HAF. Also good deal for the money.

Tip of advice also, don't go with a seagate hard drive. Try to go with Western Digital, as they are very reliable.

Your PSU is fine, antec is a reliable brand.

Can you post links to where you might buy these parts?

Really, a very good list of parts.
I recently used that motherboard and a i3-3225 which went together well.

You will need some ddr3 ram, at least a 4gb kit, but preferably a 8gb kit with two sticks.

The Antec is a fine psu, but a good 400w unit will power a GTX550ti.
That said, you can buy a Antec 650 green for $40 after rebate:
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

If you can stretch your budget a bit:

A SSD will make everything you do feel so much quicker.
A 120gb ssd will hold the os and half a dozen games. Is that sufficient to abandon a hard drive completely?
A intell 330 or samsung 830 will cost about $100.

I really like the ivy bridge duo's for gaming.
But for gaming, the graphics card is all important. My rule of thumb is to budget twice the cost of the cpu on the graphics card.
Using that rule, you might use a GTX650ti and a G850 cpu.

You say you "scrounged up" those parts; from that I assume that's what you have in-hand and are ready to build (or you already built it). If that is the case, you have a decent but modest system, which should be able to play most games, although you will probably need to lower graphical settings somewhat, especially if you play at 1920x1080.
If you have NOT obtained those parts yet, then this is what I think of them:

ASUS DRW-24B1ST/BLK/B/AS Black SATA 24X DVD Burner
Fine.

COOLER MASTER Elite 311 RC-311B-SWN1 Silver Steel / Plastic ATX Mid Tower Computer Case
Crappermaster has been proven to be dishonest in competent technical reviews. I cannot ethically recommend ANY of their products, in any category, no matter how good. Although my opinion of their case quality (vs. utility) is low, that's not relevant to the point I want to make.

SAMSUNG Spinpoint F4 HD322GJ/U 320GB 7200 RPM SATA 3.0Gb/s 3.5" Internal Hard Drive
What is the warranty on this drive? One year? AFAIK, only some of the Western Digital Black drives are still offering five year warranties. Furthermore, the WD Black will be much faster than the F4. The F3 offers similar speed, but has that miserable one year warranty.

EVGA 02G-P3-1559-KR GeForce GTX 550 Ti (Fermi) 2GB 192-bit GDDR5 PCI Express 2.0 x16
This card is a little weak for modern games. If you need to make a tight budget, there's a MSI HD6770 (only slightly stronger) for $80 on Newegg right now if you can buy from them. Otherwise, improve this as much as you can. Buy a HD7770 at the least, and a HD7850 if you can.

Antec NEO ECO 620C 620W Continuous Power ATX12V v2.3 / EPS12V 80 PLUS Certified Active PFC Power Supply
Fine. This is a Seasonic-built PSU, so I would expect it to be reliable and produce clean power. It's a little more power than you need, but it will sustain any single-GPU upgrades you're likely to want over the next few years.

ASRock B75M LGA 1155 Intel B75 HDMI SATA 6Gb/s USB 3.0 Micro ATX Intel Motherboard
Fine. I've been generally pleased with ASRock.

Intel Core i3-3220 Ivy Bridge 3.3GHz LGA 1155 55W Dual-Core Desktop Processor
While an i5 would be nice, for gaming on a budget, benchmarks suggest this would be a good choice.