Health. Massive market which isn't going away and is really interesting for new startups - because they don't have the obligation to continue sustaining their current products whilst developing new stuff at the same time.
For example, hospitals are always tight on budgets and the majority of that budget goes to simply existing and operating today and tomorrow. Very little budget and time for innovation.
Coupons -- both online and offline.
Construction -- 3D printing will be the tool of choice to disrupt it.
Insurance -- there is little transparency in the process of getting insurance for anything.
Security and Privacy -- an increasingly important thing to address.
Real Estate -- the commission that brokers take to just connect buys and sellers is nuts.
Packaging -- Amazon's frustration free packaging was a good step forward.