Juju at scale - Spinning up 2,000 EC2 instances automagically using Ubuntu's cloud tools. The thought of all that raw power at your fingertips is amazing, and unthinkable for anyone outside of a major corporation just a few years ago. We live in an age of wonders.
The TTY demystified - I never cease to learn new things about the Unix stack I rely on. This history is a good lesson in how tricky and changing requirements can be managed with good engineering, but end up freezing handling for decades-obsolete hardware in code we'll likely be using for centuries to come.
Men invented the internet - We're entering a very weird time, as computing becomes a higher-status profession it feels like women are even less welcome.
Cloudian - Layering an S3 API on top of a Cassandra hosted service. Amazon's cloud service interfaces have become a de-facto standard, and other providers should adopt them. They feel like the system calls of a distributed OS.
Tigerweb - An online viewer of the latest version of the US Census's geo data. It's a great way to explore the completely free and open data on boundaries, natural features, and especially roads that the government makes available. If only it didn't rely on Silverlight!