One of the largest and most popular online tutoring sites is tutor.com. In order to work for them, you must pass through a screening process and some tests (see Resources).
Smarthinking.com focuses on higher level learning. They cover advanced math and sciences as well as English and writing. You would need to complete their "E-structor" certification (see Resources).
Tutorvista.com has been seen on the "Today Show" on NBC. Their tutors are top-notch and have to pass their training program, which can take 3 weeks to a couple of months (see Resources).
Go4etutor.com offers one-on-one tutoring as well as all test prep courses, from ACTs to GMATs. They have an assessment period and paid training program for their tutors (see Resources).
While using a virtual chalkboard, ehomeworkhelp.com offers tutoring in the basic courses: math, English and science. Becoming a tutor for them seems relatively easy, and they even offer tutors a chance to start their own tutoring business (see Resources).
One of the most popular names in the tutoring business is Sylvan. They have Sylvan Online for grades 3 through 9. To be a tutor with eSylvan, you need to have a current teaching license (see Resources).
Be careful in giving your personal information to any company. Check with the Better Business Bureau to be sure they are a legitimate company. Most of them are real businesses, but there are some scammers out there who will try to take advantage of people.