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The quality of the domain names and logos varies wildy across the sites above - and I suspect some may be aggregating or incorporating each others' listings. But you get the idea...
BrandBucket got a bit of attention, so (I'm guessing) everyone else sitting on "brandable" domains trawled Fiverr and eLance for logo designers who could blast them out in bulk for pennies and cobbled their own version together.
Whether it works as a business model is entirely unclear - the proliferation of such sites could just be down to desperation i.e. the domains weren't selling when they were just slapped on a sales lander or text list. Or it may have radically transformed the sell-through rate. Who knows...
Brand Bucket charges $10 for getting listed, $100 (up to $500) for the logo, plus 30% commission on the sale price and they require exclusive sales rights on your domains as long as they are listed.
There are new requests there every few hours. I imagine that diligent sellers with large portfolios watch it carefully and make relevant suggestions to improve their sell-through rate.