I would highly suggest building your own machine from your own sourced parts, not a barebones kit. I usually source parts from Newegg, Fry's, and sometimes Tigerdirect. Tigerdirect has not been great to me in terms of returning rebates in a timely fashion. Also- don't hesitate to shop around on ebay for good deals on many of these items.
That i3 is really not what you want. It would be a bottleneck for your system. Ultra brand power supplies are also sub-par from what I've read and experienced. You may find yourself purchasing a new one within a few weeks/months. 8 gigs of RAM is good for now, this is something you can upgrade later if needed since RAM always gets cheaper quickly. I would definitely bump up the processor to the 3rd gen i5 at least, instead of that i3. If you plan on overclocking - you can get a 2nd gen i5
http://www.newegg.com/Product/Produc...D=3938566&SID=
How many computers are you looking to build and is $800 the total budget or the budget for 1 machine? I do this as a side business so I'd be happy to help out with the sourcing of parts (as would many others, I'm sure).
Don't forget - Black Friday and Cyber Monday will get you some good deals.
http://www.newegg.com/Cyber-Monday-D...ionStore/ID-56
Overall recommendations:
Better quality power supply
i5 CPU
8 gigs of quality RAM