i9250 is the GSM model. i515 is the LTE Verizon model.
http://www.amazon.com/Diztronic-Flexible-Revision-Protector-Packaging/dp/B0065PGWQ0/ref=sr_1_2?ie=UTF8&qid=1326418269&sr=8-2
This is a popular cheap case used by many and it fits both GSM and LTE VZ model. Supposedly it also fits with extended battery. This is Revision 3 of the case, the newest one.
Got this case yesterday. Great case for the $$. Fits the phone well, has a nice feel to it, and it has a cool glossy lip that makes the phone look good. I actually prefer the way the phone feels in my hand with this case as opposed to no case at all.