There are a lot, and most therapists these days don't only use one orientation, but are "ecclectic," meaning that they draw from several theories and pick and choose what they feel will work best with their own and also the client's personality, and also the issue you are dealing with at the time.

The various theories can be grouped into a few basic schools of thought, and many new theories have developed from the original ones, keeping some ideas, rejecting others, and adding some of their own methods.

The first well-known school of thought in psychology/psychiatry was Freud's Psychoanalysis, because he was the first one to decide to develop a method for treating psychological problems specifically. There are many Psychodynamic theories, which can all trace their roots back to this theory. These are the theories that say our problems are rooted in our past, and treatment involved exploring the past and/or working on aspects of your development, or developmental tasks that may not have been resolved in a healthy way.

Then behaviorism offered a different perspective. The behaviorists said that your past has nothing to do with anything going on right now. Instead, your behavior is related to the environment and what is happenening before and after the behavior. The first behaviorists didn't thing we could scientifically study or understand anything we couldn't directly observe, so they didn't deal with thoughts, feelings, etc. But then cognitive psychologists came along and said that thoughts and feelings are behaviors too, and they are important. So this is where we got CBT and a whole bunch of other cognitive-behavioral theories.

Another movement in psychology was Humanism. Carl Rogers was very optimistic about human nature and said that if people were free to be who they really are, then they would be okay. And we are in charge of our own actions, thoughts, decisions, etc. - not the past or the environment controlling us. Rogers felt that three things are enough to give people the chance to change themselves - we need someone to be genuine, who has empathy, and has unconditional positive regard for us as a person. Pretty much all therapists try to be like that, whether or not they also use other methods along with it.

There is also Existentialism, which came from philosophy and the goal is to help you make sense of the world, find meaning in your life, accept responsibility, and face the facts about life such as that we are all in it together, and eventually we will all die. There is a lot about avoiding things because of our fears, and this theory is about facing your fears and living your life even though it's not going to be easy or comfortable all the time. Again, there are lots of theories in this group.

There are newer theories too like multiculturalism, and specific ways to combine various theories and apply them to specific concerns.

But essentially every therapist (and maybe even every client) has their own theory whether they draw from one specific theory and try to stick to it faithfully or they combine various things. There are aspects of most of these theories that most therapists probably use at one time or another.

Hope this helps,
Rap