Pre BC has covered many options and so did Muddiver.
It goes much further than just this list. Basically, if there is water and someone has to be put in it to make a repair or do anything it is a dive position.
Watch Discovery Networks, they have a show called the Tuna Wranglers I believe. These guys have to get sharks out of tuna cages and repair nets when they tow tuna to be fattened up in ocean pins. Crazy.
There really are a few main areas of diving that communities are built around. There is a surprising lack of cross communication between them as well. Geeky white man sport tends to drive a bit of isolationist mentalities.
Recreational Diving: All things for fun and sport.
Public Safety Diving: All thing law enforcement and Fire/Rescue.
Scientific Diving: All things research related, either university, government, or private research.
Commercial Diving: Technically any job for pay while diving that does not fall into the above areas.
Technical Diving: I list this separately as it a huge grey area. Generally falls under the category of recreational diving, but the techniques and diving is finding its way into all of the areas.
Imagining Community: Does not matter what diving techniques they are using it is all about the images. So, they tend to do anything that is needed to get the shot.
All have careers and jobs in them. No matter what area, they are all jobs that require a generalist background and the wearing of many hats. There is no easy jobs in diving. But, if you learn business with the diving you can make a good living and a career out of it. For many it is joke as we have seen in this thread, but most of those that feel this way never took it upon themselves to step outside of the what will be given to me box to expand their ability to make a good living. Like so many thing in life, nothing comes to those that expect it without hard work.
It is not hard to be trained and learn what you need to be able to have a choice at working in the diving industry, what is hard is success in the diving business. This is not the fault of the industry or any group or area. It is the fault of each and every person that does not make choices and say no to what they feel is unfair or not enough compensation.
Anyway, if you love the water and you take the time to learn business along with your diving abilities, you can make a very good living at diving. It will not happen in a year as it could in the old days of IT startups or in banking, but look where they are at now.
Diving really comes down to a life of passion, if diving is a passion you can get paid to do what you love to do and share that love with others. If you are not passionate about it I would suggest you look elsewhere for your career. If you are passionate and take it seriously, you can do well and be paid.
Hope that helps.