Actually, In-n-Out has the best shakes...but you can only get chocolate or vanilla. And my new favorite is a little local place near me that has chili-chocolate shakes. Yummy!
They have Strawberry Shakes too.
In N Out also has strawberry shakes. And as a ‘secret menu’ item you can get a neopolitan shake (chocolate, vanilla, strawberry swirled).
Chili-chocolate does sound yummy!