Last Friday night, we went to the Pierpont Morgan to see one of the current exhibits and discovered that entrance is free from 7-9pm. I recommend the exhibit showing the Hours of Catherine of Cleves. Here is the review of the New York Times from January. The Morgan website has the online digital facsimile edition here. Not sure what a Book of Hours is? Here's an overview. A hypertext Book of Hours is here and you can scroll down for the Hours of the Virgin Mary.
The exhibit was quite beautiful. The 157 miniatures (two on each page) themselves accompany the prayer texts and encourage devotion. Particularly noteworthy are the details of the borders (with butterflies, dragons, birdcages, fish, plants and vines) around each. Of the book itself, the Morgan Museum says:
The Hours of Catherine of Cleves is the greatest Dutch illuminated manuscript in the world. Its 157 miniatures are by the gifted Master of Catherine of Cleves (active ca. 1435–60), who is named after this book. The Master of Catherine of Cleves is considered the finest and most original illuminator of the medieval northern Netherlands, and this manuscript is his masterpiece.