Really enjoying exploring mashups, in particular data visualisation. In the last couple of days I've come across these:
Describes itself as "A ninja tool for helping you house or job hunt within Great Britain". You put in your postcode, and it provides a map with a mask covering areas which you include or exclude on the basis of commuting distance, house price, and scenic-ness. It's currently in beta, but I signed up today and got my invite only hours later. It seems that you will soon get invites to give to friends too.
Pointed out by Kate, Dipity allows you to create interactive timelines. You can add events, pictures, blog feeds etc to a timeline, or you can add content from any RSS feed. Here's my timeline based on the BBC Technology RSS feed.
Google Public Data Explorer
Another offering from Google labs, they say: "The Google Public Data Explorer makes large datasets easy to explore, visualize and communicate. As the charts and maps animate over time, the changes in the world become easier to understand. You don't have to be a data expert to navigate between different views, make your own comparisons, and share your findings."
For example, this one tracking life expectancy at birth against fertility rate: