Actually there are dozens, but the standard 5 are:
Basic First Aid
CPR
AED
Bloodborne Pathogens
Emergency Oxygen Provider
Many health & safety organizations teach all 5, but some agencies and courses are more known than others. For example, many people talk about the "DAN O2" course, but DAN is just one provider of emergency O2 training (albeit a good one, and one that many of us support). However, many others also teach emergency O2. Likewise, American Red Cross often gets credit for first aid and CPR, but many other organizations also teach this.
Nice if you can get these classes with a diving slant to them. For example, many of the folks I work with have customized their first aid, cpr, and O2 classes with divers in mind. This is a big deal when teaching things like a field neurological, appropriate for diagnosing serious bends hits, or for in-water rescue breathing. Many standard first aid instructors do not have water skills, so this stuff is just hypothetical to them. Some agencies allow this type of customization, others do not. Also, some agencies charge quite a bit for each class; others work to keep costs down.
Personally, I teach for American Safety & Health Institute (ASHI). They have very reasonable rates on books and cards, and there is ample opportunity to teach the courses as dive-related safety classes.