Prior to my posting this answer, there were two votes for computers as to being the most infuential and revolutionary devices.  All three of these choices have piviotally changed a large portion of our lives, causing a close "Rock, Paper, Scissors" kind of situation.  While I cant completely dissagree as to the importance of the computer, I will dissagree that it was not the most revolutionary.

In order for something to be revolutionary, it must change or challenge some of the basic fundemental properties of our lives. The computer, especially in a culture of online webistie users, does seem like the most influential part of our lives but I dont think that of the three choices availiable that it is most important.  Before computers and before the interweb, people communicated in writing much as we do in our websites and forums in newspapers.  News articles, open forums, letters to the editor, and so on, all existsed in newspaper form long before our coveted computers came into our lives.  Because of this, I dissagree that computers had the most profound effect on human life and culture from the three choices.

Cell phones are important, more so than what my peers have given them credit for.  Prior to cell phones you had to be in a fixed location in order to communicate, or you had to have a really nice field radio with someone you wanted to talk to with a similar setup.  Cell phones gave you the freedom to communicate freely from nearly any point on the globe with anyone else nearly anywhere on the globe.  This didnt just make us mobile, it made us capable of communicating on many different levels.  Text messages, voicemail, email, and the internet all have simillarly been strapped to our belts, meaning that we niether have to be home in front of our computer or phone in order to communicate, but we dont even have to answer the phone to recieve vital messages.  However, even this doesnt make me belive that it has most fundementally changed our lives of the aviliable choices.

And that leaves us cars.  Certainly not the most recent invention, and certainly not the most groundbreaking, but nevertheless it gets my vote for the following reasons: It makes people migratory and it makes us consumers.  Prior to cars, peopole tended to live in one area for long amounts of time, often living thier whole lives confined to a limited geograhpical area.  While some still chose this type of live, the vast majority of people are on the move!  Vast distances can be covered in cars, shinking the world to a more manageable size.  That trip to the grocery store or mega mall could be a long walk, or even too far to make it in a single day of travelling by horse and buggy.  That would mean that most people would have to have shopping availiable to them within a very short distance in order to get what they need, and that would either limit the physical area that could be habitated by humans or it would mean more stores.  more stores would mean that they would have to be smaller, and smaller stores mean a more limited selection.  Also, the goods put on those shelves would have to be supplied in a rapid manner or two things would happen: one, an already limited supply being further limited by supply delays, and two, the fresh consumables like produce would have to all be generated in your local area or simply not be availible at all.  Without cars we dont have a distribution system and therefore our quality of life, by meaning the limitations of foods and acess to other supplies like cell phones and computers, drops off dramatically.  Also, the distances we can travel dissapears, meaning that we dont have acess to the world in a way we have now.  My vote goes to the automobile, not a revolutionary device in our own time as it was developed long ago, but as the most pivoital and revolutionary device that has changed our lives the most.