I don't think there's much anymore. I remember decades ago some products used the 60hz cycle as a internal clock of sorts, but I doubt many current products do anymore.

But the far bigger problem is that while most new products could easily be manufactured to connect to DC power, you're talking about buying a new product to replace the old one. Or significant work to retrofit. In a typical house, your furnace and A/C, major appliances, TVs, lights, garage door opener, sump pump, power tools, kitchen tools, etc etc would all need to be replaced or retrofitted. That's a huge expense. Much easier are the things that have an external transformer (cell phones, laptop, etc) where you'd only have to replace the transformer.  

In the long run, conversion to DC may make sense, but the transition would present huge problems. Each house might need to install a DC-to-AC transformer to run dual for a decade. But even running dual presents a problem because that would mean dual wiring and outlets.