Overall, looks like a decent build for the money using that site. My main gripe is the case/PSU combo...certain brands of cases come with acceptable PSU's in a package when you're on a budget, but I would maybe bump your budget slightly to get a stand-alone PSU since I don't believe Xion is one of those brands.
Here's the least expensive PSU on there I would trust that has 500+ wattage:
Buy the Thermaltake W0388RU TR2 Series Power Supply at TigerDirect.ca
Here are some inexpensive cases you can get to go with that PSU:
Buy the Cooler Master Elite 311 Red ATX Mid Tower Case at TigerDirect.ca
Buy the Cooler Master Elite ATX Mid Tower Case at TigerDirect.ca
Buy the Cooler Master RC-430-KWN1 Elite 430 Mid Tower ATX at TigerDirect.ca
So for an extra $26-$40 bucks you can have a nice case and a much better PSU.
Also, what are you doing for a video card? The onboard on that motherboard may be better than others, but it's still no powerhouse for gaming. Can handle lower resolutions and lower quality, and that was on games a couple years ago. You're going to want something standalone, and I'm not quite caught up on which video cards are better yet, so I'll leave that suggestion to someone else.
I'd also go with a newer chipset with AM3+ support. Since you will probably get a dedicated video card, you won't need the onboard, and there are some decent 900 chipset boards. Here's a few, between 80 and 130:
Buy the BIOSTAR TA970XE AMD 9 Series AM3+ Motherboard at TigerDirect.ca
Buy the GIGABYTE GA-990XA-UD3 AMD 9 Series Motherboard at TigerDirect.ca
Buy the ASUS M5A99X EVO AMD 990X Socket AM3+ Motherboard at TigerDirect.ca
They all have similar features, the main differences are the cheapest one has a 970 instead of a 990X and number of USB ports supported. First board has 2x PCI-E x16 slots vs 3 on the others, but that's a bit of a moot point, since your first board had one.
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