Once upon a time it all was free. Now you pay for some things. Soon you’ll pay for more. Here's a look at what charges you may want to consider.
Overture pioneered the paid or sponsored listing. They auction off keywords to the highest bidder. Have your bid accepted and you pay a fee for every clickthrough. The minimum now is ten cents, only Overture knows what the highest keyword rate is. These links can be valuable if you’re actually selling something on the Web.
Google has something similar to Overture's keywords. Google's version is slightly move expensive for a given keyword, which you would expect since Google gets way more traffic than Overture. But Google gets these listings up much faster and so it's better for testing keywords.
Now for the sites that charge for registration. There are more of these every day.
Looksmart, Teoma, and Yahoo are all directories where you must pay for inclusion. Of these, only Yahoo makes any business sense and then only if your strategy fits a specialized site listing in a narrow Yahoo category or if you see a Yahoo listing as important to improving your ranking on Google. Yahoo currently charges a nonrefundable $299 fee to consider your site for inclusion. If the site is accepted, you will pay that fee every year to remain in the directory.
Among the search engines, things are better, at least for now. Inktomi is charging $39 for a listing Teoma is charging $30 per year. I’m sure there will be more who will be charging soon.