http://pcpartpicker.com/p/BWxL here is all the parts for my friends pc he is looking to build in total around three months. hes wants the price below 1800 but to be able to get the best bang for the buck and be able to play all games on ultra with 60+fps. and are all the parts compatable
Everything is compatible but there is a massive overkill on PSU, even if he had 2 x GTX680 800watts would be enough. For gaming the I5 3570K would be a better choice and the money saved could be used for a min 120-128GB SSD for OS and frequent apps.
i7 is a waste of money for solely gaming, as mentioned above.
550W PSU is fine as long as it's well made
Caviar green HDD as your sole HDD is a bad choice. They are low power usage and performance, better used as a secondary storage drive rather than something you run things from.
2133Mhz memory is all well and good, but in terms of price/performance, it's not very well spent $.
Sound card is probably unnecessary but I guess it's a personal preference.
GTX680 isn't necessarily great value either, but it's still a good card.
SSD will give a faster responding system and gaming performance is almost the same for the I5 and the I7 (not noticeable difference since games do not use the hyper threading on the I7)
Make sure you have a quality PSU.