If you're not juggling *quite* that many SDs, this adapter/holder handles uSD, M2 and sim:
http://www.amazon.com/gp/product/B002Z7N0TY
I ended up picking up this reader/holder, and I expect it will remain sufficient for my needs for some time to come. In addition to the 2 uSD, 1 SIM and 1 M2 storage slots (all cards I currently use, though only one of each and usually in their respective devices), 1 more of any of the above can be stored in the reader slot.
I hadn't considered it when I ordered, but the reader is slim enough to slip in the cover flap of my NC case, which I had thought impractical for anything but a wiping cloth or a few sheets of paper. In a lot of cases, it would fit neatly in the ID pocket (fits mine, too, but makes the cover bulge there when closed).
About the only con I see is that they probably could have made it smaller still--I suspect the center 1/4-1/3 of the width is wasted space inserted for that credit card form factor.