There are a ton of good books in their store, so a lot of it will depend on what you're interested in and what your level is. I have quite a few books from them and have been happy with every one.
Practices of an Agile Developer is just the right amount of discussion of methodology, project management, and technical practices.. you know, before you get back to just writing code. :)
I have a copy of http://pragprog.com/book/rdbcd/behind-closed-doors -- it was very helpful while I was managing people for the first time a while ago.