Above, a storage bed that uses parts of IKEA's STOLMEN closet system as its basis. Initially from Stadshem.se, via Anita Sienudzi
A mattress placed over two MALM dressers works well for this Swedish boy's room. Seen on Hitta-Hem
Another STOLMEN bed hack, this time from Stil Inspiration
An even more complex build: Ikea kitchen cabinets and doors form storage and steps up to a bed in this small apartment, from Oh Yes Blog
Weekday Carnival came up with this configuration, with different colored kitchen cabinets (with dinosaur pulls!). To the left of the bed is also a combined desk.
And last but not least, IKEA Hackers shows us this version, with EXPEDIT bookshelves forming a ring around the edge.