We tried two different shoe organizers, both from Bed Bath & Beyond. The first one we tried ($19.99) was nice because you could see each pair through the clear plastic:
The second shoe organizer we tried ($29.99) was much more stable. The hooks over the doors were thinner and presented no problem with closing the closet door. By screwing this organizer into the door, it stayed put and there was no worry of sagging. This was the keeper. And look, she still has room for two more pair!! Closet simplicity step #2 - check!