Out of all of the iPod or iPhone cases I've seen, Vaja makes my personal favorites -- I bought one of their cases for my 80gb iPod, and it's still the best gadget case I've ever owned. They're a little pricier than some cases, but the exquisite leather, custom design, and solid crafting makes the purchase worth it.
And now they've introduced an iPad case as well. Of course, the iPad's use chart looks a little different -- it doesn't necessarily seem like the kind of device you'll be pulling out while walking around, and you probably don't need a great leather case if you're just going to use it as a satellite computer around your home (not that anyone knows for sure how they're going to use their iPad yet). But Vaja makes some quality cases, and while they haven't announced all of their iPad options yet (the Retro Slim Jacket is the only one available right now), it might be worth looking at if you'd rather put a little leather on your new Apple tablet.
Customization is not yet announced but likely -- when I ordered my iPod's case, there were a whole bunch of different case styles and colors to choose from. Cost on the one they've got is $120, and they're saying it takes about 25 days to get each custom-made case put together. A Vaja case isn't something to be purchased lightly, but quality like this doesn't come cheap or fast.