Gtx 670 brand differences ?

There aren't many differences that I know of (maybe number of fans, and the companies customer service) but not anything that affects performance. Basically if you have heard of the brand and it has good reviews its probably a quality brand.
I would go with Asus, Gigabyte, MSI, and EVGA.

most of them use the 'reference' card design set out by nvidia, so the performances actually don't vary too much. they do vary greatly when using original 'non-reference' designs though. the following use stock designs:

galaxy
evga
msi

don't have much to say about these. there's tons of evga fans that swear by them, but i prefer the non-reference designs. their warranty isn't as great as it used to be either. check out reviews on each brand if it matters to you i guess.

non-reference:

gigabyte
asus
palit (overclocked, ~100mhz higher than base. bit higher memory too)
zotac
inno3d

gigabyte is probably the solid pick out of the others, since their design uses three cooling fans and it runs very quiet and cool. priced very reasonably too. asus is another fab choice, the ' DirectCU II TOP' twin-fan design is reportedly just as great. massive heatsinks. would've bought this but wasn't in stock, sadly.

palit might have a lesser reputation in the states, but they're quite big in asia. not a bad pick here either, initial reviews suggest their factory overclocked card is great. they have two editions - one uses two fans and the 'extreme' edition uses three fans with higher overclocks, not as quiet as the gigabyte under full load but not that noticeable still.

not that familiar with zotac. they also have two versions, a 'normal' and an 'extreme' AMP! edition. twin fan design, was quite loud compared to gigabyte's. very bright and chunky.

inno3d's was the most expensive, and i could see why. was quite hefty with a triple-fan design, can even detatch the top heatsink cover for more air cooling. very nice quality, box said the fans were sourced from japan or something. i think it even comes with a licensed copy of 3dmark and they also throw in a mousepad. great if you have the cash.

Thanks to both of you.

I will probably go with a the Gigabyte variant (gotta love those fans).
If it runs out before I can get my mitts on one then Asus seems a great alternative .

Kinda getting paranoid about stocks of these things though =(