This is another lucrative area of the Internet you can get involved in. The simplest form of publishing is to issue small newsletters by e-mail.
Alternatively, you could set up an in depth Web based publication, which will involve more work, but you can charge more for it.
You don't necessarily have to charge, by carrying advertising a free publication should make a profit.
The content is up to you, although business, financial and sex related magazines are popular.
Include things like up to the minute news, competitions, interviews, features and reviews of other relevant Internet sites.
Charges will depend how long the publication is and how specialised the information is, but you can make customers pay by using a password system, or by taking credit/debit card details.
Don't forget to advertise your publication extensively on the Net, and use mailing lists to mailshot potential readers and contributors.