I got one off of Amazon for about $5. I love silicon cases because they are grippy, shock absorbant, easy to remove and put on quickly, and they do not scratch the phone.
However, I have noticed that when the Sensation is perfroming certain multimedia tasks, like watching Netflix, the app or phone starts to freeze or act very sluggish. When I remove the case the phone is extremely hot, so I am assuming the processing is being affected by the heat. Silicon cases act as an insulator.
If I could use it without the case it would be great. But I like to prop the phone up against something on my desk so I can work on my PC at the same time and the case allows this. Otherwise, the naked Sensation just slides all over the place.