Quick email tip from Tricks of the Trade:

If you are sending an email with an attachment, add the attachment first, then compose the message, and then add email addresses tothe send line. Now there's no chance you'll have to send the ever-popular "whoops, forgot to attach the file" follow-up.

In fact, it's a good practice to always put the email addresses of the recipients in last, to ensure that an errant carriage return or mouseclick won't fire off the message half-baked.