I love the external functions of Google Spreadsheet, which aren't available in Excel as far as I know. I think those functions are a great killer feature (and they should be highlighted and improved).

This use is very cool: Reduce those long URLs in batches, using Bit.ly
http://sharingdocs.blogspot.com/2008/12/reduce-those-long-urls-in-batches.html

What are your preferred spreadsheet examples?