I love this list:

http://www.readwriteweb.com/start/2010/09/ron-conways-7-tech-megatrends.php

  • Social
  • Real Time
  • Location Based Services
  • The Urban Entrepreneur
  • Mobile
  • Flash Sales
  • Behavior & Transactions

I looked at the current businesses I am working on and saw a lot of items that would fit. However, one interesting note was whether a startup that is focused on one space would be better than one which clearly fits into multiple spaces.

  • Vivooh (social)
  • RealTimeFight.com (real-time)
  • AtmTag.com (location based, mobile)
  • DumbInternet.com (flash sales, behavior and transactions)
  • ByTravelers.com (location based, mobile)