So, it depends on what you're looking for, and who needs it.
I like Garrett's Elements of User Experience for a nice on ramp and introduction
I like Steve Krug's Don't Make Me Think and Rocket Surgery titles for understanding basics of usability and usability testing.
I like Unger's Project Guide to UX Design for an overall step by step.
I like Wodtke and Govella's Information Architecture: Blueprints for the Web for a less prescriptive overall design process
I like Brown's Communicating Design for a great take on UX documentation
I like Kuniavsky's Observing the User Experience for a great take on ux research
I like Young's Mental Models for task focused research & great visualization & alignment of project functionality with user behavior
I like Norman's Design of Everyday Things for shifting the way you see usability and user experience in everyday life (and apply that to work)
Looking forward to Wroblewski's Mobile First, but it's not out for a couple weeks
Josh Clark's Tapworthy is a decent mobile design guide if you're only up for nuts and bolts instead of understanding internal combustion
Rosenfeld Media is a publisher that focuses exclusively on user experience and has some fantastic titles, including the mental model book already mentioned.
And of course there's tons of great online resources and events - look for local UX Camps, local UX Bookclubs (http://uxbookclub.org)
If I had to choose just one? Design of Everyday Things changed how I see the world.