I designed (in Sketchup) and built some bunk beds for my boys. They're made out of all common sized lumber, SUPER sturdy, and have no exposed nails or screws! The kids LOVE them and I'm really happy with how they turned out!
This portion of the build is just for 2 bunks, but the design allows for a third, lofted bunk to be added (I'll build that next year)
I've got the full step-by-step build at