I rarely post about work, but Xero was named one of the 10 best application user interfaces of 2008 by Jakob Nielson.
*swoon*
From the article: “But Xero might be a more interesting example, simply because it targets the traditionally dry domain of accounting. Users compared this interaction to playing Tetris and described it as fun and addictive. Come on, making accounting fun? That’s an award-winning design.”