All these suggested may not be necessary in my opinion
Samsung 8GB 1600mhz
Coolermaster HAF X
Sure these are nice components, but OP might be trying to get into gaming and won't be doing anything high end.
The Gigabyte GA-990FXA-UD3 is expensive and not needed, OP could get away with a GA-970A-UD3. Seen as there is no crossfire involved going for the 990FX chipset is a pure waste of money.
8GB 1600mhz? Go for a cheaper make, branded expensive RAM has no value for an average user. Branded expensive RAM is really for overclocking and enthusiasts. I use some cheap Eudar CL9 RAM, it does the job.
HD 7850 is depend OP what resolution will you be running at? A HD 7850 is a good choice if your into gaming at high resolution and want it to last for a few years, but if you are going to be running at 1600x1200 and under, the HD 7770 is not bad to be fair. Its a good starter card, I use it at 1440x900 and yes it can max out the latest games. A HD 7850 may be overkill depending on your resolution. If you are going to be 1080p gaming with say 22" monitor yes the HD 7850 would be suitable. It depends on res
Coolermaster HAF X is a waste in my opinion, but to be honest I don't get why people spend so much money on a flashy case, for a first build you won't be looking at the case. Go for good airflow than looks or brand. Even a cheap case with a lot of vents and purchasing a lot of decent fans would give better results over the top looking cases.
1TB HDD is useful if you plan to store a lot of videos, pictures and a lot of games. I still can't fill my 500GB drive
so depends how much you are going to be storing. An SSD will give a very nice performance boost, but only get one if you know how to manage it, that is using it for a boot drive, otherwise it may get fill and a bit sluggish quickly if you don't manage storage correct.
OS: Ubuntu won't run .exe (Windows) games natively, so you can't just open up your CD tray and click setup, you'll need to install wine. As an OS, ubuntu is a lot smoother than Windows, but again you won't be able to just pick up and go with games. So I would recommend Windows 8 just because its cheap.
What I reckon would be fine:
HD 7770/HD7850 (if you have a large monitor running at 1600x1200+)
Any DDR3 1333mhz RAM
1TB Seagate drive (if you will be storing a lot of videos and games on it)
SSD if you really want things to happen quick, if you can deal with a bit of slow copying and moving now and then a HDD will serve fine
XFX 550W power supply
The FX-4300 is not worth it considering the FX-6300 is only slightly more in price with the benefit of good multitasking and can match the top Phenom II X6 and some i5s
The CX Corsair isn't the best quality power supply
As for the case, it is personal choice, but you may regret spending a lot on a top notch case when cheaper cases can look fine and perform pretty well.Edited by mikeo01 - 11/19/12 at 9:29am