Foursquare now visualizes your check-in history (blog announcement).
Reminder: Must update http://kattera.com/4sq/
evanstoner asked: Saw your post about Sigma.js. Your readers may also be interested in D3.js. It's a pretty robust data visualization library that I've used a few times and really enjoyed.
Thanks - another data viz javascript library http://d3js.org/ + gallery on Github

Sigma.js - is an open-source lightweight JavaScript library to draw graphs, using the HTML canvas element.
NYTimes data viz: Obama’s 2013 Budget
Awesome Data Viz: The evolution of Western Dance Music
Animated map of Auckland’s public transport
Buses (teal), Ferries (blue) & Trains (red). Gets busy around 6am.