If you want to create a disruptive product then choose any "reactive" product in your industry and develop a "proactive" product that makes the "reactive" product unnecessary.
"Reactive" products are often developed when an "idea guy/gal" (call him/her: IG) identifies a pain point. Once the pain point is identified, the IG develops a product or service to take away the pain. Think of this like you would think of a chemist who develops a drug in order to cure a disease or ease an ache. Can you think of a few products or services that are "reaction" oriented -- they serve the purpose of eliminating a pain when the pain arises?
Server farms --> the solution to the pain many enterprises experience when they don't have enough space to store their electronic information on their own machines AND/OR when they need the information stored in "the cloud" so it can be accessed anywhere.
Server farms truly are a "reactive" solution to this pain point because they don't prevent the pain, they just act as a solution when the pain occurs. A product that would prevent ("proactive") the pain would be something that would prevent the small/medium enterprise from ever needing to outsource their "clouding" needs. When someone invents a way to store LARGE amounts of data on a small chip or machine that could fit in any office AND that machine has wireless capability THEN that person will be stealing business from companies like Rackspace and Amazon (among others).
Companies are often slow to prevent (be "proactive") the pain because they make so much money off of solving (being "reactive") the pain. For them, it truly is a matter of "no pain, no gain". But if you can prevent the pain all together, then the gain will be yours!
Mosquito bites? Yes, our only real solution to mosquito bites is calamine lotion. (I haven't found a great repellent, have you? And even if you have, who wants to spray it on every time you go out?) What if someone invented an annual shot (like the flu shot) that either repelled mosquitos OR when bit, the chemical would immediately neutralize the impact of the bite? Crazier things have been invented! And I think this "proactive" product would be a great seller if anyone could ever put it together to bring it to market.
What do you do when your carpet gets dirty? You lug out the Dyson, move the toys/kids/furniture out of the way, and you clean! It's a "reactive" product. Pain arises and the Dyson is there to soothe your pain...for a while, at least, until the carpet gets dirty again. What's the solution? Create a "proactive" product! Create self-cleaning carpet. Crazy idea? Maybe, but it's the start of a disruptive idea. It's a brainstorm off which disruption can be built.
Disruptive products aren't just the next step up in terms of quality or customer service. Disruptive products don't simply do a better job of solving a "pain in the pocket". Disruptive products prevent the pain from ever happening.
What industry are you in? What are the pain points that businesses or consumers feel in your industry? What current products or services "respond" to these pain points? Find a way to "prevent" the pain points from occurring and you will have a disruptive product/service, and it will likely make you a lot of money!