Make no mistake: The iPad's mail app is perfectly serviceable. It handles all manner of email, and the interface is adequate, if not inspired. Perhaps its that lack of inspiration, though, that keeps the app store bubbling over with new mail alternatives.
One of the newest candidates to replace Apple's default mail app is called MailDeck, and it has a few features that make it rise above the crowd of competitors.
For starters, MailDeck is free, though you can opt to pay $5/year to remove the narrow ad banner at the bottom of the screen and add custom email signatures. It's an iPad-only app as well, optimized for the iPad’s larger display.
MailDeck is designed with multiple users in mind. Because more than one person is likely to handle your tablet, you can set up multiple user profiles and passcode protect them, so only authorized users can browse email. It's a nice privacy feature you don't see with many other apps.
The app makes great use of the iPad's screen estate. You can display email in list view, as full message previews, or in "deck" form, where six email previews appear on the screen at once. The deck view works best, and makes browsing email feel more like scanning news stories in an RSS feed.
MailDeck has a few interesting features up its sleeve, like the ability to change an email into a task, but my favorite is the fact that the app collects all of your attachments and rounds them up in a unified view -- making it easy to browse or search for specific attachments, view them, and even forward them in new emails. Dealing with file attachments is often the hardest part of managing your email, and MailDeck solves this problem elegantly.
Perhaps the app's biggest weakness, though, is that it currently supports Gmail and IMAP, but not POP or Microsoft Exchange. That means you probably can't rely on MailDeck as a comprehensive mail replacement, at least not right now. But if you yearn for smarter email management and a more refined interface, definitely give MailDeck a try.