Rather than get one of those flip cover style cases for my Transformer Prime (it still needs a name), I opted to get a sleeve type case.
I don't remember how I discovered Saddleback Leather Company on the internets, but they sell some really nice leather items, including a wallet I picked up from them a couple years ago. Their Classic Briefcase has been on my IWantINeed list for a while now.
When it came to sleeve cases, Saddleback Leather was the first place I went looking and was delighted to find their Gadget sleeve. I had to wait a bit for the colour I wanted to be in stock though.
Although the sleeve is sized more for an iPad sized tablet (the Prime sticks out some), the Prime still fits in there pretty nicely with some additional room to spare. A Prime with keyboard dock would probably go in there perfectly.
For now, the case holds the Prime in pretty securely so there's not too much danger of it slipping out accidentally. Even with some light shaking the Prime stays in the sleeve. That may change as the sleeve gets broken in over the next year.
The stitching is pretty solid, and if it's anything like their wallet, will take a lot of abuse before it starts showing any sign of wear. The leather is 2 mm thick, and the inside is lined with pigskin (I think). It should provide a good bit of protection against falls, unless it happens to fall on the open end, in which case you'd be pretty much hosed.
This sleeve case is likely to outlive every gadget I'll ever own.