iReceiptMail is a program that integrates email read receipts into Mac OS X Mail. The app communicates with Apple Mail and allows you to request a read receipt for your emails and, at the same time, notify the senders when you read their messages. If you want to ask a recipient for a read receipt, simply enable the option from the menus once you are ready to send the message.
Mia for Gmail (was Notifier Pro for Gmail) is a desktop Gmail client which sits politely in your menu bar.
