We have this "funny spot" at the top of our stairs. We decided to custom build a desk for our girls computer. It fits perfect, better than anything we could find pre-made. Built from 3/4" birch.
The best thing about this desk is it gives our 12 & 15 year old a tiny bit of privacy but we can walk up the stairs and see what site they are surfing or if they are really doing "homework" at anytime.
Better yet is the cost....about 1/4 what you would spend in a furniture store! We built another in their room for homework, writing, drawing etc. It takes up far less space than a standard desk but still gives plenty of room to work. This one has a white board as a backer. Our youngest LOVES white boards and dry erase markers. It also has under shelf lighting, no need for a desk lamp!