I'm holding out hope that a FreedomCase is released for the SP3. It's the only case I've found that leaves the back of the SP3 uncovered while in use, so heat dissipation is not reduced. It looks like it would be really comfortable for laptop use as well.
I got a nice leather one off ebay. Real high quality leather d-Park one. It is tan with a black flap, maybe not everyone's colours but I like it. There is also black with a light blue leather. The flap gives you a place to clip the pen. I like natural products with a nice leather smell but also it is very soft and very robust. Stitching is top quality. About $30 off ebay.