Hi Folks! I bought my SGP5.0 back in January and still learning my way around it. Its a neat lil gadget and a good choice over the 7+ I was looking to get. Discovered it at the last minute as Best Buy was selling it as an MP3 player!
While at BB, I too wanted a case to keep it in and scoured the store for something that would apply. They had this Nintendo case which works great!
POWER A Pokemon Zip Case for Nintendo DS Lite
Inside it has 2 elastic bands to keep the game secure. For the 5.0, I cut out the upper band as it's not necessary, as the 5.0 will fit rather snuggly in the case. For me to get it out, I just push from the bottom and it pops out. Thats how snug it is! The other half of the case easily holds up to 2 styli and 3 memory cards.
The down side is it does not have a belt clip, but for day to day it does the trick and the case will protect your 5.0! And it's 10 bucks!
If you need a case to carry everything, then go to Walmart for this slightly larger case:
POWER A 3DS Mini Transporter Case Blue 3DS Nintendo DS Dsi
The front compartment has a nice pocket to hold your 5.0 with a velcro strap, and styli. The back half can hold 12 memory cards, or if you don't need that many, there's room for your usb cord and ac adapter. This case has a handle that you can loop your belt through to keep it at your side. At the store it was in black as well as blue, and cost $15.
I hope all this helps. I too checked online, but did want to spend a lot of money on a case or wait for Samsung to make one.
BTW, try one of those small picture frame stands to hold your 5.0 landscape style for watching videos/movies! You'll have to add those little rubber cushions to keep it from sliding, and you may have to shape the stand to better hold the 50, but it works and can be carried easily as it folds.