an aluminum case will be a good alternative to ordinary cases, like leather cases, plastic cases, etc. it can be found here:
I think it is the best case i ever tried on my N95.
The original leather case from Nokia is very nice, but does not protects too much when it's opened.
The crystal cases are too cheap and fragile.
The rubberized cases are better than the crystal ones, but still fragile (two months and they're broken).