I don't have one myself, but I've been eying the
Incipio felt sleeve for the K2. It's available from the mfr and from Amazon for $20, though shipping may be cheaper through Amazon.
I'm thinking of getting a skin as well (I'm halfway between wanting a leather book-style cover and going with a sleeve/skin combo) though I haven't found a skin I like much.
DecalGirl skins seem to be the best, but the only solid color one they have is black. The skins are $15 from DecalGirl, and you can also get ones from
SkinIt for the same price (though the cutout is different) or you can design your own for $20.