The only other cover that I've come across in brown that looks anything close to decent quality (in pics at least) is
this Natural Hemp one. Handy if you're looking for an animal friendly one too (if that's your thing).
But I wanted the look and feel of a traditional leather bound book, hence the choice to go with
Noreve. I've gone with a dark brown full grain leather which should get better with use as a patina builds up to give it character. To my mind another good choice would have been a beige/cream cover which would contrast nicely with the Espresso brown of the device. The only drawback of that might be that as a patina builds up, it could just make cream look dirty rather than adding character, but I could be wrong.
So you could either go for colours that tone with brown, but that contrast like beiges and creams. Alternatively other pale versions of colours like pink, blue or green should go with brown and look more contemporary.
Thinking about it, my going for dark brown and trying to match the espresso probably wasn't a smart move. It could just end up looking like it's trying to match, failing and therefore look wrong, but never mind, I'll see how it turns out. It's a shame they don't do a rich burgundy; that would work too; and I like burgundy.