Here's an option to consider:
[url=http://pcpartpicker.com/p/Sf3J]PCPartPicker part list[/url] / [url=http://pcpartpicker.com/p/Sf3J/by_merchant/]Price breakdown by merchant[/url] / [url=http://pcpartpicker.com/p/Sf3J/benchmarks/]Benchmarks[/url]
[b]CPU:[/b] [url=http://pcpartpicker.com/part/amd-cpu-ad580kwohjbox]AMD A10-5800K 3.8GHz Quad-Core Processor[/url] ($114.99 @ Amazon)
[b]Motherboard:[/b] [url=http://pcpartpicker.com/part/asus-motherboard-f2a55mlkplus]Asus F2A55-M LK PLUS Micro ATX FM2 Motherboard[/url] ($59.99 @ Newegg)
[b]Memory:[/b] [url=http://pcpartpicker.com/part/gskill-memory-f31866c9d8gab]G.Skill Ares Series 8GB (2 x 4GB) DDR3-1866 Memory[/url] ($64.99 @ Newegg)
[b]Storage:[/b] [url=http://pcpartpicker.com/part/toshiba-internal-hard-drive-dt01aca050]Toshiba 500GB 3.5" 7200RPM Internal Hard Drive[/url] ($54.99 @ Newegg)
[b]Case:[/b] [url=http://pcpartpicker.com/part/nzxt-case-gama001bk]NZXT Gamma Classic (Black) ATX Mid Tower Case[/url] ($29.99 @ Newegg)
[b]Power Supply:[/b] [url=http://pcpartpicker.com/part/corsair-power-supply-cx430]Corsair Builder 430W 80 PLUS Bronze Certified ATX12V Power Supply[/url] ($34.99 @ Newegg)
[b]Optical Drive:[/b] [url=http://pcpartpicker.com/part/lite-on-optical-drive-ihas124-04]Lite-On iHAS124-04 DVD/CD Writer[/url] ($17.99 @ Newegg)
[b]Monitor:[/b] [url=http://pcpartpicker.com/part/aoc-monitor-e2051sn]AOC e2051Sn 60Hz 20.0" Monitor[/url] ($89.99 @ Newegg)
[b]Total:[/b] $467.92
[i](Prices include shipping, taxes, and discounts when available.)[/i]
[i](Generated by PCPartPicker 2013-04-21 23:15 EDT-0400)[/i]
* CPU/GPU = APU is the best for the $ right now.
* Mobo has what you would need for this budget range.
* RAM is fast and has LOW PROFILE heat spreaders, so you will have the option of adding just about any CPU HSF on the market to your mobo. You could drop down to 4 gb's of RAM, but with an APU I would recommend sticking with 8 gb's, since your iGPU will use some of that RAM to run.
* HD is good and $10 more gets you 1 TB, so you can decide on that.
* Case is simple and will do the job for this budget.
* PSU is a quality one and will allow you to upgrade to a dedicated GPU down the road (up to AMD 7850 or nVidia GTX 660).
* Monitor is 1600 x 900, so it's a bit better than 1366 x 768, IMHO. Another $10 gets you 1920 x 1080, but that will be up to you if you want that. I like 1920 x 1080 when it comes to working on a single monitor. I can split the screen up to 2 x 970 x 1080 windows. This makes multitasking a bit easier, IMHO. You can decide on what is best for you.
I'm over budget by $17, so you could drop the RAM down to 2 x 2 gb's (4 gb total) and save about $30, but I'd recommend against it, if you have that option.
If you upgrade the Monitor to 1920 x 1080 and upgrade the HD to 1 TB size, the build price would be up to about $487.