W. Wikipedia
The go-to source for information on almost anything, its hard to imagine how the world existed before the birth of Wikipedia, an encyclopaedia of several million articles (and counting) that are editable by all, but heavily moderated to ensure factual accuracy. Though it may be forbidden as source material in academic circles, informally, its value is unrivaled. Honourable mentions go to Wikia, a site that allows users to create specialised, small-scale Wikipedias for whatever subjects they desire, from Lost to Lego, as well as Western Union, which has evolved with the times, allowing users to transfer money across the internet in a matter of minutes in emergency situations.
X. Assorted Sites Of A Particular Nature
Without going into too much detail, the web is a haven for a particular industry, which according to Forbes Magazine, owns 4% of the worlds top million websites, and is the result of 13% of web searches.