Personally I can taste fish sauce in most cases when it is used in a dish, but apparently it's rather common for people to not notice it, nor the "fishy" smell. It's a bit strange considering fish sauce by itself has a rather distinct and pungent odor. I've been playing around with it off and on in recipes, but I can never really say that I *like* it all that much. Fish sauce and sesame oil are kind of overkill for me, when in most cases I would rather just use some soy sauce.
Smoked paprika is a favorite of mine, because it packs so much flavor - especially when compared to regular paprika. It adds a nice "meaty" and smoky taste and aroma to even the most bland dishes.
Of course, using Mayo to "butter" bread for grilled cheese sandwiches works surprisingly well too. At first I was concerned it would make the sandwiches greasy, but actually if you think about it, mayo is oil combined with other ingredients, whereas oil and butter are basically 100% fat, so it's technically slightly less in fat.