Here' a Google map gadget.

Here's a Quote of the Day Google Gadget

Here's an interactive map. People can add places they've lived into a spreadsheet, and it will automatically update the map below.

Here's an business application of google spreadsheets.  The user can enter stock symbols and use spreadsheet functions to dynamically access the price of each stock, its PE ration, and its eps.  It can then graph the results. The data is constantly updated as is the graph.

Here a way to make flashcards for students. To use this gadget, from the spreasheet insert tab, select gadget and search for the flashcard gadget.