What is a good internet business to start?

When it is about business or generating revenue, internet helps you in 2-3 main ways

1. Search Optimization:- Once a system is connected to an internet, if a person needs to look for something specific, either that person has to be given the specific details like URL or IP address. With a lot of services already available, provided an independent search engine is always useful. A search engine acts as a portal for the user to get into the internet.

2. Most of the internet based applications acts as an intermediary for people with common interest. That is when applications flourish, to make a seller meet a buyer. Applications can connect a service provider with a service requestor. It connects an employee with an employer. Hence, if the business requirements for a specific online application can be captured correctly, you can have a website to get the people with similar interest to get on-board. Bayt.com itself is an example for this.

3. Internet for channelised information - In this approach, we build an application for specialized purpose and we can streamline all information for that specific expertise to reach a specific group of people. The website or web-application would mature with the industry requirements.

Online specialized skill or certification providers are an example here.

I like to add to the answer given here that you can start a subscription based specialized membership site where you generate good and useful content through videos, articles, posts, quizzes, competitions, events, games and so forth for a specialized group of people (whether in the same geographic location or regionally / internationally).