Ask HN: Resources/Advice for Relearning Math

It has been 25 years since my last math class and as I get more into programming and DSP I am realizing how much I have forgotten and even for what I remember I often suspect that I don't really understand, just am able to dredge enough out of my memory to get things to work. Any good sites or books aimed at people like me, a good crash course starting in algebra getting to calc? Or is it best to just start from scratch and start with a pre-algebra text book working my up into calc textbooks?

At my current level I can generally figure things out and the code does what it should but it takes a fair amount of trial and error and the result is probably not that good.