If you're tight on space, then shelving is an essential -- and displaying photos or artwork under the shelves is a neat trick for getting even more out of your limited room.
Fashion blog ThreadBanger details how combining a standard shelf with an IKEA magnetic photo rack made for an easy way to display (and change) photos or artworks. You could adopt the same idea with hooks or other display options, but the ability to swap with magnets makes it particularly appealing. Got your own preferred way of displaying photos? Give it up in the comments.