"Getting Things Done" by David Allen. I'm sure everyone here is familiar with bits and pieces of GTD methodology, but I encourage you to check out the full text. There are a lot of great ideas in there there that I didn't find reading online about GTD. I have been a serious GTD user for more than a year now, and I feel amazingly more in control of my life. Everything I've done in that time - from planning my wedding, to projects at work, to completely organizing my house - has gone smoother than I can remember projects going ever before.