If you've ever meant to send a file to someone only to receive a reply mail that you forgot to attach it (and haven't we all?), this tip may be just the thing for you.
An enterprising add-in developer for Outlook 2007 and Outlook 2010 has created the beta Outlook Attachment Reminder, which checks your mail for customizable keywords such as "attachment" and "attached" and prompts you if you try to send the mail without actually attaching any files to it:
Please note that this add-in is not supported by Microsoft; download Outlook Attachment Reminder at your own risk. If you do install it, restart Outlook and then check Add-Ins, OAR Addin, Options:
There you can review and change the settings, including the addition of any other words you use when attaching files:
As you can see, it can even remind you if you forget to enter a subject line.