Are there any situations in which drones may legaly fly higher than 400ft? FAA FAR 107 states, "The maximum allowable altitude is 400 feet above
  the ground, and higher if your drone remains within 400 feet of a
  structure."


Are there any exceptions to this rule that would allow a drone to be flown at a much higher altitude than 400ft AGL or within 400ft proximity of a tall structure?



source
As they say with any regulation, there’s a waiver for everything.  If you do wish to operate your sUAS at or above 400’ AGL, you are advised to contact the local FSDO in your area.  Protocol varies from area to area, but you will be required to file an request with local ATC with the dates, times and areas you intend to operate in so NOTAMS can be issued.