nopFlexible is a responsive template with advanced navigation and it needs testing by the nopCommerce community before it finally goes for sale.
***Edit*** I have decided that this theme should be a contribution to the nopcommerce community and it is now free
It would make a good basis to make a responsive nopcommerce store.
Please test it on your devices - the layout and menus are completed and there will be some cosmetic touches before completion over the next few days.
See this thread for free version