I even got a list:
PALS, ITLS, NRP, PEPP, ACLS, AMLS, GEMS, AHLS, NALS, PPC, ABLS.
First thing, congratulations on wanting to learn the "ALS assist" skills, and wanting to educate yourself further. You're the sort of person I would want as an EMT partner. Not being happy with what you know, and wanting to learn more to do the job better is the right attitude to have. It will make you a good EMT and a good medic.
But, don't mistake these alphabet courses for real education. Often these are courses you have to take for ongoing licensing requirements, or to meet job application requirements. Most of them, as others have pointed out, are very light on detail and understanding.
If you can get any of these free, go do them. For sure. If you want to educate yourself further, take some basic science courses, especially anatomy & physiology, and go to paramedic school. Teach yourself to interpret 12-lead. Some opinions / rambling:
I take ACLS mostly because I have to. And every medic probably should. Keeping a current ACLS card is a basic mechanism that shows that at least some point in the last couple of years you've spent a few hours looking over the guidelines. Granted, they're already available on-line for free. But it shows you've done some professional diligence. As an EMT, borrow a book, read it.
PALS is a mixed bag. It's also very simplistic. It's focused on cardiac arrhythmias, which are a relative rarity in the pediatric population, and cardiac arrest. I think it's worthwhile as a medic, because most of us don't see this population often enough. This is a situation where you can't prepare enough, because unless you have a large body of experience with sick kids (I certainly don't), they're stressful calls. But... PALS is very limited.
[PEPP and PPC aren't really on my radar. I've taken both at different points, and got the feeling that PEPP was more directed towards BLS. I don't know if this was the particular course I took, or if it's all PEPP courses. Sometimes the "alternative" courses are less structured, whereas AHA stuff like ACLS and PALS is required to be delivered in a certain format that prevents the educators from actually dealing with other relevant areas. PEPP might actually be worth taking as an EMT. As a medic, I wouldn't pay for it. I would pay for PALS]
NRP / NALS -- I was under the impression NALS was just the old name for NRP? NRP is very simple, but it's a good course. It's just very very basic "what to do when you deliver a flat baby" material. It strongly emphasises PPV if the neonate is apneic, and compressions if PPV fails to resolve this quickly. That's 90% of NRP. But it's like PALS. How often do you do these calls? When will you do your next one? It's a low-frequency high-acuity event. These are things we should train for.
AMLS - didn't like it. Borrow the book, see if you find it valuable. I wouldn't pay for it.
AHLS - is interesting. But I wouldn't spend my own money doing it. I don't think that it's particularly useful at BLS, unless you're involved in a hazmat program. I think a firefighting hazmat course focusing on de-con is probably more useful for most people. Few of the medications used are routinely carried on ALS cars. Relatively few systems have an ability to deliver them in the field within a reasonable time-frame. It will probably take a large incident with loss of life until this changes. As an EMT, I'd skip this completely. It only makes sense for medics.