These days you can study most subjects online, although there are a few that are not available. That being said some degree programs are a lot more popular than others. As a result these tend to be the easier ones to find a school to study with. There are of course good reasons why these are more popular, they tend to be the ones that have the most direct connection to a career field.
As a general rule the most common online degrees are the ones that are aimed at working professionals in order to help them advance in their career. Because of this most of the degrees that are offered online tend to be at the Masters level. There are of course lots of degrees at the Bachelors level as well but you will find that you have more options for graduate study. The obvious reason for this is that most of the people with jobs who need to take advantage of online learning already have a Bachelors degree.
Because most of the people who study online are doing it to upgrade their career it should come as no surprise to learn that business degrees are the most widely offered. There are actually quite a few different ones that cover all aspects of business but by far the most common is the Master of Business Administration. Almost all schools offer this one since it is the most widely sought after of the business degrees.
Another very common online degree is a Masters degree in nursing. This is one of those cases where there are no undergraduate degrees available since this is the kind of field that you really have to have hands on experience to enter. That being said once you are working in the field getting an advanced degree is pretty much a requirement to move ahead. As a result there are all kinds of degree programs that cater to nurses who are looking to get promoted to the next level.
Engineering degrees are similar to nursing degrees in that they are only available at the graduate level. Again this is because of the necessity of having hands on experience to enter the field. Most engineers will find that they need an advanced degree to move into more senior positions. In addition since it is a field that is constantly changing it is usually necessary for them to return to school mid career just to learn the latest developments in the field.
Teaching degrees are another one that fall into the same category as nursing and engineering. You will need to attend school full time to get the degree that you need to enter the field. However in order to improve your career prospects you are going to have to get a Masters Degree. Therefore there are a lot of online schools that offer these types of degrees.