Santa Maria della Angeli is a unusual little church not far from Assisi. It is famous for its relation to St. Francis and is, I believe, a pilgrimage church.
Inside the church is relatively plain, compared to many of the churches that we visited in Italy (or elaborately decorated, compared to American churches I am familiar with--context is everything). One very notable feature is a smaller church built inside the main church, which was a church where the first Franciscans used to gather.
This church also has some important pilgrimage sites. There is a rose bush that Francis reputedly threw himself on which retracted its thorns (some of our party thought it might actually be a Camellia, but who knows), and probably most important, the small, rude cell in which Francis spent the last days of his life. That is pretty neat, and it is very, very basic.
Associated with the church is a major bookstore dedicated to St. Francis. This store has a significant selection in English, not just of tourist books, but of all kinds of learned books and even children's books. We spent a lot of time browsing in the store.
If you are highly interested in St. Francis, this church is a must-see. If you have little or no interest in Francis (but how could you if you are visiting Assisi?), you might want to skip it.