Notes: I picked up all these parts from my local Microcenter store, which is why my selection may be odd. He needed it built same-day.
I got a 500gb HDD because he did not want a hybrid setup, and his previous HDD size was 250gb. He only used about 10% of the space on his 250gb HDD, so a 500gb HDD worked out perfect. He's getting a lot of games now, which is why I didn't get a SSD. I didn't go with a terabyte because he will never use a terabyte, and it's extra money that could be put towards something else (Like the SD card reader).
The z87 board was the best one at Microcenter that I could find for the money, and had the best reviews. I would've picked a different board if I were purchasing online, but he needed this PC same-day.
Went with 700w PSU because the 500w PSU's were cheap-quality, and I did not want to run the risk of frying the mobo.
I went with Nvidia because I've had bad luck with AMD products in the past (Overheating & failing within a year, even with the proper cooling), so I didn't want to risk his gpu failing prematurely.
My really good friend's PC recently died on him (Broken PSU, PC was around 7+ years old), so I built him a new PC just in time for Christmas. Plays all the games he wants at max settings without any lag (Skyrim with HD texture pack, Need for Speed Most Wanted, Battlefield 3, and F1 2012.)
Used the Windows 7 key from his previous machine on this one.