Handmade Modern: A Lofted Bed You Can't Find In Store - What a great way to save space with multiple use functions. All kids love bunkbeds. My child has a full size bed and complete bedroom suite and would rather have this, haha!
This is a perfect combo of my two favorite ideas for that space under the stairs leading to the basement. A reading nook AND book storage and shelves . assuming that there is enough space for this there.
At the back of the dining room area you could put a wall-to-wall bookcase filled with books. If you don't have that many books you can have a display bookcase where you place nick backs, a few books, some magazine, sculptures etc.