Switzerland. All of It
Via, Simon Willison, a fully interactive map of Switzerland. This sort of server interaction without page reload is shaping up to be the big web technology of 2005. A few months ago I saw my first example, a simple search-term predictor for someone's weblog (unfortunately I didn't bookmark it). Now we have Google Suggest, Gmail, and now this map. PHP.net recently added a similar search-term predictor to their PHP function-list search. This is a fairly major step in the evolution of web-based applications. Expect to see the same technology utilised by Amazon and Ebay by the end of this year.