Google Spreadsheets finally added charts. This feature has been developed for many months and was one of the biggest lacks from Google's spreadsheet application.
You can create more types of charts: columns, bars, lines, pie, scatter, add labels and a legend. Just select the columns you want to plot and click on the new chart icon. After inserting the chart in the spreadsheet, you can save it as a PNG image or edit it.
The charts are rendered as SVG in Firefox/Opera and VML in Internet Explorer, so they don't require plug-ins. As usually, Opera is not officially supported, so you'll find things that don't work as expected.
You can annotate cells and search using Google the text from a cell.