A time-tested spacesaver, the loft bed is perfect when square footage is limited. Some stylish options:
Above: Photo via My Scandinavian Retreat. (N.B. For more creative design ideas for children's rooms, see "Children's Rooms: Indoor Climbing and Sliding Spaces.")
Above: A loft bed in New York via AT Casa.
Above: A children's room in Hampstead by London architects Stiff + Trevillion.
Above: A children's loft bed by London-based Studio Mama.
For DIY loft bed ideas, see "Bedroom: Built-In Loft Spaces."