If you ever delete any of the stock Adjustment Presets supplied by Aperture you can do the following to get them back:
First Quit Aperture
- Go to folder ~/Library/Application Support/Aperture - That is your home Library folder. In Lion that Folder is hidden so to see in Finder do Go->Go to Folder, in the window that opens enter ~/Library/Application Support/Aperture press return
- Move the Adjustment Chain Presets file to the Desktop
- Restart Aperture
The factory presets should be back.
Note: if you have any custom presets you should export them before doing this and then import once the stock presets are back.