You didn't have optical drive, and didn't know if that was intentional, so have included one.
I have increased RAM, using faster. So cheap it's not worth not having 8GB, and single stick wasn't ideal.
Whilst B75 boards are OK, they're more aimed at business use, although not huge difference.
Given you much better power supply, and better case.
The MSI is probably best value HD7770.
If you can, consider using a 120gb SSD instead of a small hard drive.
That will be large enough to hold the os and half a dozen games.
It will get you started and make everything you do feel so much quicker.
If you need more space for large files, you can add a hard drive later.
Intel and Samsung are having sales to deplete the inventory of 330 and 830 ssd's in anticipation of the new 20nm based 335 and 840 series. You should be able to find one for <$100. sales abound this time of year.
malbluff's build should be good. if you can spare 20 more bucks, you can pick up a evga gtx 560 which will perform a lot better
Is the GTX560 still ahead of HD7770. I seem to remember this same discussion, on another thread, and someone had benchmarks, based on the latest catalyst update, showing HD7770 ahead of GTX560. Wish I could remember where it was from.