Fast Money

If your host allows you to have commercial banners and advertisements on your site (most domain hosts do), there are a variety of companies that will pay you for placing banners or buttons or sometimes even search boxes on your site. Generally, there are four ways to generate revenue:

Get Paid -every- time you show an ad: usually referred to as CPM (or cost per thousand shows), this was a once common form of advertising on the Internet. For smaller sites, it seems to have died off, although a few sites still pay it.
Get Paid -every- click on an ad: usually referred to as a CPC (cost per click), this is probably one of the most common forms of advertising on the Internet. Usually payout is from 1 cent per click to 25 cents per click. This means you will get money any time someone clicks an ad on your site.
Get Paid -every- signup for a service: usually called a CPA, this is a form of payment for when someone does something, such as fills out a form or orders a service.
Get paid Commission: Payment when the someone buys something through your link.
And, of course, an obvious way to make money...
Selling a Product or Service Online