I would recommend the JG Matrix - I have it and am slowly introducing it to my son (you need to be able to count to 20 and back before you can do any actual sums, and we're stuck on 1-2-3-4
)
The program is very simple compared to the more flashy and commercial curricula, but it does the job and I expect it to be very successful. It is similar to touchmath in that it introduces dots on the numbers to count the quantity of the numeral.
I have also looked at MEP, though I would say it would help a lot in the later years if I were familiar with the modern teaching techniques for the various topics. The problem is that the way they teach various things (like long multiplication/division) is not the way we were taught in school. But it has complete lesson plans for up to age 16 (I think, maybe later) and I will definitely be using it, at least partially!
Rightstart looks good, and I've heard great reviews - it is much more hands-on (the other two I've mentioned are more workbook-based). I'm seriously tempted to get it in a year or so if my early-learning budget can be stretched that far!