GMail can export all of your contact information to a CSV file that can be imported by a spreadsheet application, but as far as I can tell you cannot selectively export only the email addresses. GMail exports the entire contact database. To do that:
Click on the Contacts link in the left sidebar of your email page. Click on the Export link found on the right corner of the contact listing. Set the option to export All your contacts (below the drop down menu,) then set the option to export for Outlook and other applications. Click on the Export button. The CSV file will be downloaded to your Downloads folder.
If you then import the file into a spreadsheet you can selectively remove the columns of data you don't want in order to keep just the information you do want.
