Yes, for a brief period of time, Gmail Labs’ Undo Send feature lets you recall a message after you send it. To enable the feature, open your Gmail Settings, go the Labs tab, enable the Undo Send lab, and Save Changes. You can then specify the send cancellation period, between 5 and 30 seconds, in the General tab of your Gmail settings.

Note that your Google Apps administrator must enable Labs for your domain for this feature to be available.