I'd appreciate some non-branded gear so I could individualize the design of my stuff. I.e. it's pretty hard to find good solid color/ no logo rashguards.
The major brands you find in any onlinestore you want, but if you had some non-branded stuff, maybe additionally offering printing for your customers (I bet a lot of gyms would be interested to have their own logos on the gear of their athletes), you would stand out of the mass of onlinestores.
I'm not sure as to what brands you should carry, but how bout putting up real reviews on the brands you carry? Not just what the manufacturer says. I bought a pair of century gloves that tore up with less than 5 uses. Next time I buy, I want to know before I waste my money.
I train in either Venum or BOLT MMA fight shorts. Both are quality but obviously Venum being the big name that they are are fairly high priced, BOLT are a bit cheaper but quality (although think they only sell on their website, I've not seen them retailed anywhere else).