What do you think of my build? (Only the internals)

CPU- AMD FX 8320 (stock clocked 3.5Ghz)

GPU- Gigabyte R9 280x WIndforce cooler

MOBO- Asus M5A97 R2.0

HDD- Seagate Barracuda 1TB

SSD- Samsung 840 EVO 250GB

PSU- Corsair CX600M

CPU Cooler- Cooler Master Hyper 212 EVO

RAM- Kingston HyperX Fury

Whatchya think?

Looks great! The motherboard is a little lackluster, but overall it's a great build.

Good balanced build. I think it will serve you well.  

which motherboard would you have recommended then?

Depends. What are you using it for.

Primarily gaming and the budget would be between $100-$200.

We have the same mobo, and I manage to get 4.4ghz OC. You should be fine with that mobo, until you decide to crossfire and OC by bigger margins, to which I would get a better mobo for.

I would have went with the Asus M5A99FX Pro R2.0. It's a far better board for a marginal price increase.

http://www.newegg.com/Product/Product.aspx?Item=N82E16813131851&nm_mc=AFC-C8Junction&cm_mmc=AFC-C8Junction-_-na-_-na-_-na&cm_sp=&AID=10446076&PID=3938566&SID=

Nice build overall, but you should really get a better power supply, like 750 - 800w, 600w should in theory be enough for the 280x windforce, but i have that exact card and i had to replace my cx600m with a 750watter before the windforce would run properly, (ie without BSOD, cutting out, crashing etc.)

Sorry to put a dampener on things, but since i had a near identical build i felt obliged to tell you what i had to do.

Weird.  I have a slightly less wattage system (i5-3570K @ 4ghz, HD 7950/R9 280) and a 550w power supply.  Everything runs just fine.