Cauli mash is brilliant (and very cheap) - I chuck a load of frozen florets in a saucepan and boil into oblivion. I then usually mash it up with a big lump of butter, some salt, pepper, spring onions and occasionally grated cheese. It's very close to the real deal and you can always add a bit of real potato to it to make a hybrid mash.
I hadn't thought about grating the cauliflower - every recipe I read always talks about using a food processor but it seems so obvious now you've mentioned it. Apparently cauli rice works better as a fried rice rather than boiled rice substitute.
Another indispensable find for me has been shiritake noodles - and you can guarantee these are going to become more expensive as more people discover them. They're noodles made from a type of yam and they are basically calorie and carb free but fill you up, they're basically just fibre. They look a lot like glass noodles. I find they're better than 'real' medium noodles in noodle soup as they down leak a load of starch out and make the soup and noodles turn to mush (although I still prefer real, thick udon noodles for this).
I think also if you properly dry and stir-fry them, they change from being like glass noodles to more like regular ones in terms of texture and colour. So you can also use them in spag bol as well if you're so included, or of course, just as part of a regular stirfry. It's important to cook them with something flavourful - they're a bit like tofu in that otherwise they don't taste of anything. They do also smell a bit funny when you get them out the pack so it's a good idea to wash them first.
Other more random ideas are you can make a very tasty breading for chicken out of ground up pork rinds (the puffy ones that are a bit like prawn crackers, rather than the scratching kind). You can also de-carb a pizza either by using a tortilla as a base, or if you're feeling carnivorous, make the base out of mince seasoned with parmesan and garlic.
Also, here's a treat that isn't really low-carb but is fantastic. Cook up some bacon bits or pancetta in a saucepan and put to one side. While the fat at the bottom is still hot and liquid, throw in a load of popcorn kernels and then pop the corn as normal. When done, chuck back in the pancetta, sprinkle over some parmesan and oregano, mix it all up and you've got a popcorn that's way more fun than the usual salt or sweet flavour.
