No matter what diaper bin you buy (and I've tried a few), it's pretty much impossible to get one that doesn't end up smelling. I leave mine out in the rain for days to try to rid it of the stench, which ends up being just a temporary fix.
I recently discovered a cure in dryer sheets. Take a Bounce or Downy sheet and put one in the bottom of the container. Every time you open it, you will get a whiff of fresh linens or flowers instead of something heinously stinky.
This tip also works for cars, shoes, and anything else malodorous.