I wouldn't do flip flops. Even though I live in them at home, all the standing and walking at WDW really took a toll on my foot. I had a lot of pain and when I got home, I got a tendonitis dx. A year and a half later, it's still bothering me.
Since you won't do Crocs (who cares what they look like, they're comfy!) I would suggest some water proof sandal/tennis shoes. I can't think of any brands off the top of my head.
I think the key is to make sure you break them in before your trip, and to alternate them with another style once you're there.