It all depends on website/content, user country and other stuff. You can get from a few cents to a few dollars (there is no exact ammount).
Even within a site the lowest and highest amounts can easily vary between a few cents to nearly 2 dollars. That's how much it varies for me, anyhow. The average is what's really interesting - but it would be against the TOS to say how much it is (for me). Let's put it like this: closer to the cents then the dollars.
even within narrowly-defined niches, the clicks vary widely. one niche i have will swing between $1.00 to $.06 per click. generally, though, for my niches i suppose i get something like $.27 per click.
It depends on what type of ads are being shown. Your website's content, visitor's country etc. also matters.
The advice, as often given here, would be that you should create a site based on your interest that you can write a lot of interesting things on.