My Budget Build
I am doing the same thing right now with a similar budget in mind. I wanted to build something easy to transport, as well. With the new Ivy Bridge cpus being capable of running games at low to mid setting with no discrete card, while also allowing for a massive upgrade ceiling, I chose to go with that if possible. Here you can see the i5 3870k running Diablo 3 on high settings at 1280 x 1720 res:
http://www.bit-tech.net/hardware/2012/05/28/intel-hd-4000-investigation/5
While this is not that impressive, it is still playable at those settings. Turn down graphics to low and/or drop some res and gameplay will become smooth.
The main advantage to this is upgrade potential. With the lower range geforce 600 series cards scheduled to arrive in the next couple months, it won't be long before this build can be converted into an enthusiast range rig.
I have been able to find a complete list of components, minus the hard drive, for an i5 rig for under $450. Here is what I have come up with so far:
http://cart.microcenter.com/cart.aspx
If the link above fails to direct you to the cart, then here are links to each component:
cpu -
http://www.microcenter.com/single_product_results.phtml?product_id=0388577
mobo -
http://www.microcenter.com/single_product_results.phtml?product_id=0387629
cpu cooler (good deal but you could gety away without this and just use the stock cooler that comes with the i5) -
http://www.microcenter.com/single_product_results.phtml?product_id=0315397
case with 300w psu-
http://www.microcenter.com/single_product_results.phtml?product_id=0330535
ram -
http://www.microcenter.com/single_product_results.phtml?product_id=0382101
dvd burner -
http://www.microcenter.com/single_product_results.phtml?product_id=0382892
All of the items will say "out of stock", but I don't think they truly are. You can still add them to your cart from their respective category listing. If you have a microcenter around, they have hands down the best pricing I've come across. I did the same process on Neweggg and it was more than $100 more for the same stuff.
As for the drawbacks: no graphics card, measely 300w psu, and no hard drive.
GPU - I would wait on graphics card until prices fall and new tech comes out. Just see how the i5 performs. It might surprise you.
PSU - Here I went with the cheapy 300W because it is only $12 more with the case. It is all we will need for a rig with no discrete graphics card. If an upgrade is desired, or becomes desirable, I found a good deal on a Rosewill that has a strong single rail for providing a powerful, future gpu with plenty of amperage:
http://www.newegg.com/Product/Product.aspx?Item=N82E16817182200. Remember: that total wattage is less important than the amperage capability of EACH 12V rail. For less than $100 it is sometimes difficult to find good amerage output on 12V rails.
Cheap hard drive:
http://www.ebay.com/itm/221039344953?_trksid=p5197.c0.m619
Very nice hard drive for decent money:
http://www.newegg.com/Product/Product.aspx?Item=N82E16820148443
Hopefully you have a mirocenter nearby to take advantage of their prices. A couple of the products cannot be purchased from their online store. If you do have a miocrocenter nearby, make sure to pre-order, or at least print up a page of your cart so that you can take advantage of the specals that are exclusively online.
