There are many opportunities for online tutors in subjects ranging from mathematics to language. Possible students are many and varied. You might teach your native language to people living in other countries via VoIP. Another possibility is to tutor schoolchildren, high schoolers or college students in a subject in which you specialize. You can work with an online tutoring agency or set up your own website to begin.
If you are looking to make a few extra bucks online but don't want an actual job, you could always fill out surveys. Many researchers offer a couple of dollars for filling out surveys for them. Some companies will pay you via PayPal while others will send you a check.