The nicest ones are at www.vajacases.com

They make cases for lots of PDAs, mp3 players etc. They are exquisitely well made leather cases. Expensive and it takes a while to get them (many are custom made, you pick color etc) but the quality, craftsmanship and design are the best I have seen by a wide margin. They fit like gloves. Ive had a number of them for various devices as has my wife. I wont even look at other cases now if Vaja makes one for what I am looking for.