The Top Five Apps
Chrome or Safari? Well, I actually go back and forth, but right now Chrome is my go to (maybe reassessing soon since Safari in Mavericks has some nice new features). Chrome is a solid and reliable browser with all the bells and whistles you need from a web-browser. Kind of cool how all the preferences and settings are actually HTML pages. Neat eh?
Living Earth Desktop
If you have some CPU cycles to spare, this is a great way to impress. Living Earth puts a relatively accurate picture of the Earth from space right on your desktop. I've actually found it surprisingly helpful in glancing for incoming storms and how much daylight is left (checking the time is so lame).
All work and no play makes any developer a dull boy. OpenEmu is the best way to waste some time. Need your Zelda fix? Legend of Zelda for NES right now. Can't agree with your coworker on whether you pronounce it "gif" or "jif"? Dusty Diamond's to the rescue. Sega Genesis? Nintendo 64? It's all there.