I guess I'll have to do a more scientific study of this smelly topic - my personal survey of 5 kitties is not a sufficiently diverse population!

You've mentioned lots of good ideas - food ingredients, litter box style and location, litter ingredients etc. Thanks for your contributions!

Although not smell-related, I have my litter boxes all setup within larger plastic pans to help contain the flying particles when a kitty gets enthusiastic about covering.

I also noted that while sharing a house with a newborn human, I noticed the smell of the diaper pail quite often. However, the baby's mom seemed to always notice the litter box smell... I guess if it's your baby, you don't mind the smell as much!