This is a good, almost academic but fairly practical article on the drivers of disruptive innovation, with some good examples of disruptive innovations:
Charles Schwab: Traditionally, stock brokers were trusted advisors that consulted the well heeled on their investments for a fixed percentage commission. Charles Schwab came along and offered less service for a low flat fee. Today it has a market cap of $20 billion.
And also of sustaining innovators:
Apple, contrary to popular belief, is not a disruptive innovator, but an incredibly successful sustaining one. They seem to have a knack for finding categories that can be vastly improved. They find an existing customer base who’s ready for more and then they dazzle them.
Apple is a particularly revealing case because they don’t disrupt industries, just the companies in them. They didn’t kill MP3 players, or mobile phones and they won’t kill tablets. Instead, they just get lots of people to buy Apple.