Newegg a10 build suggestionA10-5800K
Alternate moboAsus F2A85x-M
$99Mushkin Blackline 2133 2x4gb
$59, 1.5v and overclocks pretty good on trinity, but still high already. I'd suggest the sammy green 30nm but you didn't seem eager to oc the ram, nor is is easily identifiable on newegg. Its really good for the price if you do the work to get it clocked high to benefit the gpu. The ram can also be changed for some 2000 or 1866 mem if you are trying to slim the budget down slightly, but its going to hurt the gpu performance slightly
For the other build parts it seems you've got them (psu) or have idea's for them (case). I don't think any trinity system needs a full atx board, the need for lots of vrms isn't there, you've already got a gpu, so the only time full atx is helpful is where the slots are loaded with other things than gpu's. m-atx boards also let you run smaller cases, which is nice. Trinity also works well with small cases.
The cpu side overclocks ok. Its not at FX levels of OC but with a decent cooler, 4.3-4.4 is do-able on most chips.
The gpu can also be OC'd and that typically goes over 1ghz pretty easy. Memory controller is good too. That ram can do 2400mhz if you're willing to work for it, other wise 2200mhz is pretty quick/easy.