To this day I'm still annoyed that Apple discontinued the silicone back covers. They were my favorite kind as far as fit and finish. I tried about 5 different cheap-o Amazon back covers for my 10.5 and hated them all, including the Khomo, but I LOVE my Tech21 back cover that I eventually bought at the Apple Store. It fits perfectly and doesn't let any dust or debris in between the cover and the iPad. It also never gets fingerprints on it, which is pretty amazing.
I've been tempted to get one of the leather sleeves. They're super nice. But I've been able to withstand the temptation so far.