Ok so if he isn't oveclocking he won't need the aftermarket cooler, the stock will do fine. Even with a light OC the stock cooler is fine. Most people can get the E8400 to 3.6ghz with a voltage bump.
I'd personally go with any case the provides good cable management, most cases like that aren't cheap. IE Antec P182, Antec 900
Never skimp on the PSU, especially modular ones. There's a decent Corsair 520w modualr PSU 129.99. But it has 3 rails instead of one uber one.
Skip the sound card?? never!
OS right, how could i forget 99.99.
So minus the Afertmarket Cooler, and adding the OS it'd come to $1,263.90 If he chose the cheaper PSU subtract $27 for a total of $1236.90
Acer AL2216Wbd Black 22" 5ms Widescreen LCD Monitor with HDCP support 300 cd/m2 700:1 - Retail 229.99 Bringing it up to 1,493.89 or 1466.89 with the other PSU
http://www.newegg.com/product/product.aspx?item=N82E16824009094
Depending the the quality of Keyboard/Mouse he gets will depends on how much overbudget he'll be. Then he'll have to decide on where to skimp.
Options are:
Cheaper Case at the cost of cable management.
Cheaper Mobo, ASUS P5K series recommended.
Graphics card would be the last thing i downgrade. Same with the processor since one model lower is only $10 cheaper. However if worst comes to worst in terms of budget...
Can step down to a slightly cheaper Sound Card at the cost of game performance.
And of course he could go with a 20" monitor for a fair price drop.