One of the reason, which I believe, for someone to delete presence from Internet could be, especially after Mr. Snowden exposed PRISM, that many companies know that more the data they have, more the money they will make. Take example of Facebook, it has almost all of your data, where do you live, what you like, your friends, your family, everything! So may be just sake of privacy you want to take this step which, mostly, can't be undone!
Whatever your reason is, respecting it, I will tell you easy method to delete all the Internet accounts.
One of the obvious solution is to Do it Yourself, just move to optout page of your service provider and delete your presence from the world wide web, though this isn't easy but its most reliable solution.
It is, even for me sometimes, difficult to find the URL which will help you to delete your account so, like many other tech-savvy free solutions by techies out there, here too you have awesome services such as www.accountkiller.com, just visit Account Killer, select your service provider, it includes all of the major websites.
Once you have selected the website, you would be provided account removal URL with step-by-step method to delete your account.