Parallax
I've talked a bit about Freebase over the last few months. I understand that a rich, semantic, structured database of knowledge is not something other people get excited about, but that happens to be my thing.
In the hope to excite others with Freebase, I recommend that you spend 8 minutes watching the Parallax browser in action. That kind of research tool is only possible with something like Freebase on the bottom.
Update: the code for the Parallax browser is open source now.
