That's a pretty generic request. What are you looking for? Just a rugged case to stand up to the rigors of a gym? A case that allow you to hold it while doing something else? A case that allows you to attach it to a piece of equipment? Armstrap? How are you planning to use it at the gym? Watching a movie while on a treadmill? YouTube videos on how to properly lift? As a music player?
I respect your decision and interest. To me, the SP is a computer, tablet, and note-taking device. It's expensive, mobile, and in my case - very powerful for my work. But, it is in my opinion, too big for my particular taste for use with my workouts (size & weight & cost of repair).
Therefore, may I suggest an alternative?
If your goal is a WiFi + media consumption device (movies, music, e-reader, and browser) while on the treadmill / bikes - why not spend a little to get a BlackBerry PlayBook ($60-$70 on Craigslist) and you can load Kindle on it for e-reading, it has built-in media player for movies & music as well as a browser. It is 7 inches and while it's a dead device (no more investment in the platform) it is perfect for those types of situations. The cost of it is far less than repair of your SP, IMO. Other choices may include a Kindle Fire or if reading only a mono-Kindle for $40.
If you're diehard on the SP - eBay and Amazon have a large selection. Keep in mind, many of those cases don't afford the best airflow that the SP will need if running videos. eReading shouldn't warm it up too much.
If it were me - I'd opt for a smaller, less expensive, lighter device.
Good luck in your quest - both for a case and for your physical health!
The moko rotary case adds good protection. But as the other poster said, this device might not be best solution to what you trying to do. It will work but the risks outweigh the benefits imo. If anything I'd recommend the moko case and extended warranty on the pro..lol good luck on decision.