Toys. Burglars generally don’t bother to look for money in kid’s bedrooms. A stuffed animal with hidden cash sewn in or an envelope taped to the bottom of a toy box will frequently be overlooked.
Picture Frames. Hide money behind a picture frame on the wall.
Rugs. Almost nobody will look under the center of a carpet (the edges, maybe; but not the center: too much work).
Electric sockets. There’s a lot of unused space behind the switches and electric outlets on the wall. How to hide money in a socket? First, turn the main power off! Place the stash in the corner and insulate it with a tape. Be careful, failing to insulate anything made of metal you put inside a socket may cause a short circuit.
Upholstery. How to hide money in the underside of chairs and sofas: Remove the staples, fit a couple of Ben Franklins inside, staple again.
Books. Avoid encyclopedias; old hard-cover romance novels work well.