I've found that interesting ideas come mainly from current life experiences combined with something that happened to you in your past. By this I mean current inspiration (ex: weekend snowboarding trip) that brought about a great idea for a product, then that idea is refined by your beliefs of what you feel a great product should really be. These beliefs are mostly derived from your childhood believe it or not. But most of all interesting ideas come from finding interesting things in the day to day grind.