Enterprise Integration Patterns is #2 on a Top 10 list of enterprise books.
eWeek Magazine has a series of articles called "Pings and Packets." It seems to be kind of a blogish recap of recent news tidbits. In any event, it has started to include a list called "Amazon.com's Top 10 Enterprise Books." There are lists for December, November, and October.
Looking at the list, it seems to include any computer books with "enterprise" in the title. So an architect study guide and an EJB book make the list, but Core J2EE Patterns does not. In any event, Patterns of Enterprise Application Architecture is #1 on the list and EIP is #2. Pretty cool.
Top 10 Enterprise Books