You could create every document, spreadsheet, and presentation you work on from scratch, but if you're like me, you'll likely spend more time futzing with the file's layout and design than entering the data that comprises it. That's why I rely on the many free templates and extensions for my favorite productivity apps. I've written in the past about places to find add-ons for Microsoft Office, but there's also a wealth of free extensions and templates for OpenOffice.org's Writer word processor, Calc spreadsheet, and Impress presentation program.
Start at OpenOffice.org's Extensions page. Click one of the options at the top left to list the extensions by application, category, popularity, or other criterion.