As an avid net user I often wonder who actually manages, decides on
sites and profits from it beside individual advertisers.

Thanks for asking!

"One of the greatest things about the Internet is that nobody really
owns it. It is a global collection of networks, both big and small.
These networks connect together in many different ways to form the
single entity that we know as the Internet. In fact, the very name
comes from this idea of interconnected networks.

Since its beginning in 1969, the Internet has grown from four host
computer systems to tens of millions. However, just because nobody
owns the Internet, it doesn't mean it is not monitored and maintained
in different ways. The Internet Society, a non-profit group
established in 1992, oversees the formation of the policies and
protocols that define how we use and interact with the Internet."

How Stuff Works
How Internet Infrastructure Works - An illustrated tutorial by Jeff
Tyson
http://www.howstuffworks.com/internet-infrastructure.htm

Who decides on sites? The owners or creators of those websites. The
Internet is one of the most equalitarian societies, ever. Joining it
is as simple as creating a website, and announcing it to an interested
audience. Web hosts, those who own the servers sites are hosted on,
profit from payment for the lease of web space directly to site
owners, or advertising revenues for use of free space.

To learn more about the hardware used on the Internet, as well as
revenue models, page through these How Stuff Works  tutorials on
individual components, and web models. All tutorials are easy to grasp
and beautifully illustrated, with all technical terms explained.

Internet Hardware (5 tutorials, including the Infrastructure tutorial
above)
http://www.howstuffworks.com/category.htm?cat=Hardwar

Internet Connections (6 tutorials, Modems, DSL, Wireless, more)
http://www.howstuffworks.com/category.htm?cat=Connect

Web Revenue (7 tutorials, eCommerce, advertising, ASPs)
http://www.howstuffworks.com/category.htm?cat=Revenue

I hope this information helps you understand how the Internet works.
If you have questions, please feel free to ask.

- larre -

Thanks for enriching my understanding. 
 Your answer is perfect!

Here's a pretty good explanation of how everything fits together.
You'd probably be most interested in the section with links about ISB
backbone providers. I could type it all here, but I's probably just as
easy to leave you the link.

http://navigators.com/internet_architecture.html

If you're interested in who actually manages large parts of the WWW
technological infrastructure developments (such as protocols, language
standards), take a look at the W3C (World Wide Web Consortium):
http://www.w3.org/Consortium/