The book of Psalms is actually divided up into five books [1-41, 42-72, 73-89, 90-105, and 106-150]. Some say this in order to liturgically reflect the themes and narratives in the Pentateuch. Whatever the case, the divisions were very important to the editor(s) of the Psalter.
So, along with other psalms, I'm trying to write a song for the first and last psalm in each book of the Psalter. Here are several of my meager efforts thus far.