iOS: Outlook is our favourite email app for iOS, and today it gets better integration with the other Office apps to make editing a breeze. Provided you have other Office apps installed (Word, Excel, Powerpoint), you can now open attachments directly from Outlook, edit the attachment, then attach it back into the reply email in a snap.
To open an attachment, just tap the "Open in [Office app]" button, make your edits, then tap the back button to send it right back over to Outlook. You still technically leave the Outlook app to do all those edits, but it's integrated so smoothly that you'll barely notice.
Outlook (free) [iTunes App Store]