Club Nintendo Stars Catalogue^^
What constitutes "useful" stuff is up to you, of course. To me that is a soundtrack CD and I'm waiting for the already-confirmed-for-CN-Japan MK8 double CD.
That's the thing, a lot of the physical stuff in the stars catalogue is just a bit crap looking. I did get the Zelda wash bag thing a few months ago, which I have been using as a 3DS case, but apart from that there has been nothing I have been interested in.
Wait until September. I have seen so many people whine about spending all their stars on these when that plastic Blue Majora's Mask light was added. Don't add yourself to that pile of people.
I will probably wait just like you both have said, as you never know, something amazing may get added before it closes for good.