MailTones at $2.99 is a bit pricey, but it's a great idea and may suit a particular need you have. It lets you assign different sounds to different e-mail senders and uses the iPhone's push notification to alert you when you receive important e-mails. This is apparently the only app that offers this function. And in their just-released update they've added a feature popular with IT managers: messages to their pagers can be forwarded to their iPhones and use a unique sound to alert them that they have a support call that needs attention. And if they're sleeping when that alert comes through? The new version has an extra-loud-and-long alarm tone just for that purpose. MailTones is also now compatible with the second-generation iPod touch.