Easily the hottest reward at Club Nintendo is the Nintendo 3DS Game Card Case. The first time it was in stock a couple months ago it sold out almost instantaneously.
As of yesterday the Nintendo 3DS Game Card Case is back in stock at Club Nintendo. You will need 250 coins to pick it up and I can promise you it is worth every one of them. The case, designed like a 3DS game case, holds 18 total games in it. You can fill all the slots with 3DS games, all with DS games, or mix-and-match between the two. No current case I have seen in stores is able to do this.
As an added bonus, the Nintendo 3DS Game Card Case includes four double-sided card covers that feature Mario characters, Zelda, classic Nintendo and more.
Go grab a Nintendo 3DS Game Card Case at Club Nintendo before Wario swipes them all.