Just so you know BF3 and Black Ops 2 will not run in ubuntu even with WINE and if you're using Linux Nvidia all the way. AMD drivers are getting better but there are still more issues with them than Nvidia's drivers.
TF2 and minecraft work awesome on Linux. I'd go as far as to say better than windows based on my personal experience. I would like to point out again that generally Nvidia drivers are much better especially for games in linux, AMD seems to have more issues than Nvidia on this front. Were you using windows I would reccomend AMD cards but Nvidia is the way to go on Linux right now. As a side note do not use open source drivers for either card.
sandisk extreme 120 or the sandisk extreme 2 120, sandisk 128g for price, one is a 550 read 510 write the other is a 550 read with a 340 write. I personally only care about read speeds and product life
http://pcpartpicker.com/p/1qZaM leaves you with $50 for case or you can just swap out the GPU in another reccomended build for an Nvidia equivelent. The current games available on linux aren't that hardware intensive and linux itself is really light compared to windows. If you are going to dual boot with windows and linux the AMD cards will probably be a better choice.
ssds - crucial m5's, kingston hyperx's, sandisk (latest ones), anything intel, anything samsung, plextor. Anything but old OCZ drives really.
At 1080 the 760's are a perfect match for your rig, decent enough price etc.Linux nvidia drivers work ok,(well they do on my old gtx580 linux box anyway).
There are some good cases about that are cheaper or around the Diablo's price - bitnfenix shinobi, corsair 300r /400r/ 350D, cm storm enforcer. Worth a look anyway I reckon.