Can't make this list without mentioning Microsoft. This company created by Bill Gates is a stranger to no one. The creators of the famous and most used operating system series, Windows revolutionized the field of computing with their products. Probably one of the most known companies of all time, second to only McDonald's maybe.
A company that is second to only Microsoft. Created by the iconic Steve Jobs, invented the GUI and somewhat simplified the world of computing.
The understated creators of the programming code Java. Now one of the most used programming languages of all time, which can be run on any system.
Mostly known for their state of the art processors (leading with Intel Core i7), has made sure that computers have been able to grow with the speed and size requirements of the world.
Not necessarily a computing company, but how can you leave Google off this list? Not only have the well known and widely used search engine, they are also the designers of the android OS which is mostly used in phones. They have also provided easy ways for advertisers to show their products and web owners to earn money. Revolutionizing the web in the process.
Notable mentions : IBM, Dell
Two oldies, but goodies. Without these two companies, I doubt the level of technology would be as high as it is today.