Any of the basic poly flip ups would work like the Magpuls linked to above. I've been using the Ruger Rapid Deploy flip ups on several guns including the KSG and they have worked great. Oh, and an EoTech does work nicely on the KSG. I got mine used right here in the INGO classifieds.
Link to the Ruger sights Ruger® Rapid Deploy Rear Sight-ShopRuger Ruger® Rapid Deploy Front Sight-ShopRuger