Hmm, that's an interesting question. I have found a few little things that work, but I'm not big on brand names, especially ones that come with a huge price tag. For instance, I don't buy Pearl Izumi stuff, just too expensive. I buy my clothes from AlertShirt.com and target, and honestly, they've held up really well for me. It might be nice to stock some really downmarket clothing, but I bet it's not viable due to low margins.

Brooks saddles.
Planet Bike Superflash for blinkies. OTOH PB isn't 100%; I have a SuperSpot that I think is useless.
A good reflective vest for commuters; Harbor Freight as an excellent one for < $5, you could just resell those for $10 and people would probably not bother looking to HF to get them.
L&M has good lights.
I think B&M lights deserve a look if you really want to address the serious commuter. Not cheap but may be the best out there, and lights like the Ixon IQ are actually a good deal for the money.

If you really want to be the utilitarian's friend, have at least a demo of an Xtracycle, maybe even a Surly Big Dummy. And trailers. Not sure if there's a good retail source for utility trailers (maybe Burley?) I don't have one myself but if I lived a little closer to town I'd want one to do larger grocery/materials runs.