DS8 likes the "Key to" series. He did "Key to Decimals," "KtPercentages" and "KtFractions" last year for a class he took, and he loved it. He's on "Key to Algebra" now. The first booklet is integers and order of operations, so it's really starting with pre-algebra. There are 10 booklets in the algebra series, if memory serves.
The caveats:
> This is not creative problem solving. It's basic.
> We tend to skip a lot. It looks like he's going to finish the first booklet after only about 6-8 days of school work--maybe 3 or 4 hours of work, if that much. He's flying through it.
The pros:
> Visually, they are black and white and free of distractions, which seems to appeal to him for some reason. (This might be a con for some kids, so be warned.)
> They're cheap, similarly priced to Singapore.
> They limit new things inroduced per page, so that I can feel confident that if he can do the last 4 problems on the page, he really hasn't missed anything.
> It's very nuts-and-bolts, which suits him. Sometimes I feel like I have the same problem with math curricula for him that I have with fiction for him: he can read the book and understand it, but it's not really made for him and it seems somehow inappropriate. This feels like it fits his age and his intellect. I can't really explain why, but that's the "mom gut" feel that I have. And he often does more math than I assign just because it's fun for him. So I think there's something to this, at least for his case.
> I'm using "Key to Algebra" as a preface to AoPS. I think it's vital that he get the problem solving eventually. But he's not a speedy processor and I'm afraid if we went straight to AoPS, it would overwhelm him. Hopefully if he gets the basics down enough with the "Key to" series, then he can make better use of the deeper thinking required of him in AoPS.
> Taking both "Key to" and AoPS also means he'll spend longer on algebra. If it goes well, I'll do the same with geometry. That means I can slow him down some. Wahoo! That works for me!
HTH!