I use Smart Cover from the Playstore. There is a Lite version also.
I've used this on my previous S3 and now on my LG G2 and it works great for me.
Current Phone: LG G2 (Tmobile, Giv Mobile, unlocked)
Retired Phones: Motorola Razr Maxx, HTC Rezound (After 3 replacements, early retirement), HTC Incredible, Tmobile Samsung S3