In my dream world, I will find the ideal math curriculum and stick with the same one through prealgebra. Ds is very bright and picks up math concepts quickly. I'm wondering what is considered the most rigorous math curriculum(s) for the elementary years?

Define rigor.
In math education some people define rigor as working systematically through sequential skills with plenty of repetition. Some people define it as strong focus on logical creativity, building the ability to adapt and apply mathematical concepts to new problems and increasing levels of complexity. 
With Singapore, what do I need? I assume that I would need the Home Instructor's Guide, Student Textbook, Student workbook. What about the extras: Intensive Practice, Challenging Word Problems, Extra Practice, Math Express, Brain Maths, etc.? It's so confusing to me! We're probably looking at level 1B or 2A to start. What manipulatives do I need? I can't find a list of recommended materials on the Singapore site, but maybe I've missed it.
Thanks for all your help!! 
With Singapore, what do I need? I assume that I would need the Home Instructor's Guide, Student Textbook, Student workbook. What about the extras: Intensive Practice, Challenging Word Problems, Extra Practice, Math Express, Brain Maths, etc.? It's so confusing to me! We're probably looking at level 1B or 2A to start. What manipulatives do I need? I can't find a list of recommended materials on the Singapore site, but maybe I've missed it.
Thanks for all your help!! 
I am interested in this progam for my students tell me more.
we have been using Singapore for years and are just reaching the end of it. We used the textbooks and the workbooks, because starting around 4a, I have the kids go over the the textbook by themselves to learn the concepts and the additional problems and reviews in the text book made sure we covered every topic thoroughly when they were a bit tricksy. I can't speak highly enough of challenging word problems, but i am not sure the new editions are out yet. we also do a bit in intensive practice. we are mathy and like the HARD problems! an important note, it really helps to understand the pictorial method of problem solving that Singapore uses. this allows children to solve much harder math problems w/o using algebra. I didn't know this at first and ended up teaching my boys basic algebra just to be able to solve some of the word problems in CWP4. I found joining the Yahoo singapore math group to be quite helpful.
NM, I found answers on the web site after searching a bit more.
I seem to be one of the few here who loves Saxon math. I know it can be repetitive, but the repetition really does aid in mastery. For what it's worth, I am a math person myself (finished top of my math class in Naval Nuclear Power "A" School) and I consider Saxon top notch. I will say I don't care much for Saxon K. By kindergarten my kids have been ready for the 1st grade workbook, so we just skip Saxon K. I hope you enjoy using whatever you choose!
We use MEP too. If you are looking for advanced math concepts taught early on then I would recommend looking at it.