The Office 2007 ribbon redesign (on video)
Microsoft hasn't gotten the credit it deserves for breaking with the past in Office 2007.
I've already written positively about my experiences at Microsoft's MIX08 conference in March. It had a wholly different feel from any Microsoft event I've attended in years.
There were lots of interesting sessions but I wanted to draw your attention to one in particular: The Story of the Ribbon, given by Jensen Harris. The video is online (requires Silverlight). The reason I liked it so much is that Jensen gives a really great historical tour through the evolution of the Microsoft Word interface and explains why and how Microsoft decided that they needed to start with a (mostly) clean sheet of paper.
Microsoft hasn't gotten the credit it deserves for breaking with the past in Office 2007. In fact, they've taken a lot of heat and generated no small glee in competitive circles for putting users through such a dramatic user interface shift. However, it seems unfair to, on the one hand, consistently harp on Microsoft's lack of innovation (and many do, with some justification) and then turn around and hit them with brick bats when they do head off in a new direction.