Cyber Slide Pad Cover for 3DS by Cyber Gadget. This is a set of soft plastic covers to give your 3DS slide pad different, presumably grippier textures. The covers range from nubbly, to nubbly-with-smaller-nubblies, to an imitation of the PSP controller, to ridged. The set even comes with a case that attaches to the 3DS via strap.
I haven’t really had a slipperiness issue with the 3DS, but who knows? Maybe it would be nice to have some different textures going on under my thumb.
See also: More accessories