I'm in the same boat as Nano-Passion. I'd like to teach myself calculus. I'm a few years out of college, so I'm now brushing up on the prerequisites.
It's been slow-going for me as well, but personally I've found that the hardest part is not self-motivation or knowing if you know the material, but finding the right resources.
The best series of books I've found is the Master Math series (
). A mathematician from the 1990's named Morris Kline has also done some interesting work, and I may return to him.
I've dabbled with the courseware at a website called Rapid Learning Center - the site has a good idea, but poor execution. I can't recommend it, but it's not worthless.
I've also found that it's important to know how you learn. I read, create notes in PowerPoint slides that summarize the principles, constantly digest and synthesize the material, visually map it out, relate it to other areas I know, and then review it in some other form, book, or media. That tends to work for me. When I learn something that way, I know that I learn it, and it's personally rewarding.
The internet is great as well for supplementary material, and in a sense it's made teaching professors less relevant. b/c when you have a problem, you can simply google it - even if you're studying graduate work, if you don't understand something, chances are it's a difficult concept, other people have had the same problem, and someone else has created an answer or video that makes sense. But the internet probably isn't sufficent alone to teach yourself math, b/c the info - even if it's in depth - is unorganized.
I've sunk a lot of time in finding great reference books or even well-written textbooks. For me, it's clear that when I finally find the right ones, taking a formal course is not all that important. It's just that so many main-stream books are geared towards helping out with courses or tests, so good books are hard to find, but certainly exist.
I find a lot of coursework boring and inefficient. I roll my eyes when I see an alphabetical list of key words at the back of a chapter. Key terms are necessary, but it's more to important to know principles, and how terms relate to principles - not how they relate to each other through their spelling.
Anyway, that's just me. Would be interested in other resources, ideas, tips.