Why Open Science failed after the Gulf oil spill – The description of this researcher's interactions with the media rang very true. They took his reports and "eliminated a lot of the caveats and limits that Asper placed on his own results".
Sigma.js – An interactive network graph library, with support for both live force-directed layouts, and importing more complex structures from the desktop Gephi application. It has some very stylish visual defaults too.
Accumulo – I'd missed this Apache database project until now, but I'm interested in their take on the BigTable concept, especially their focus on security controls. Intriguing that it came out of the NSA too.
Visualizing live event broadcast delay – Working backwards from website traffic at different locations to figure out the broadcast delay for a TV commercial.
Online Hex Editor – Does exactly what it says on the tin. I don't know why I'm still amazed by how effective web apps can be, but it's striking how few barriers there are to replacing desktop programs.