Quit the web

You may want to quit online services that you don't -or don't want to- use anymore but "delete account" links are sometime hidden.
The most famous example is Facebook of course, they REALLY hide the link and offer instead to "deactivate" your account (not delete)

This page, as I'm quitting a lot of services, list theses direct links or instructions

Quit Facebook

delete your Facebook account: https://www.facebook.com/help/delete_account

Quit Foursquare

Topic on the help center page
You must connect to the website and go to settings then privacy, and it's at the bottom of the page

Quit IFTTT

delete your IFTTT account: https://ifttt.com/settings/deactivate
It says "deactivate" but means delete!

Quit Slideshare

Go to the preference page in the "edit information" section there is a link at the bottom of the page

Quit YouTube

Quitting YouTube seems tricky, because you must unlink it from your Google+ account. That is my case. But I don't know how to do it if you register to YouTube through your Google+ account. I guess you must delete your Google+ account?
So first I unlinked my Google+ account from my YouTube account: in account preference -then advanced- then I tried to delete my YouTube account, but I got an error saying it's too early to delete this account.
You have either created this channel or closed another account too recently, please try again later.
So I decided to remove all the content, channel and playlist.