The Boxer iOS app is similar to Mailbox in that it gives you swipe-friendly access to advanced inbox features. But Boxer takes it a step further.
Swipe a message to the right and Boxer lists a menu of five items. Options include Quick, which gives you a list of canned responses such as "I'm on it and I'll follow up shortly." You can also add your own canned replies. With Boxer you can also delegate an email to your to-do list or forward the message to a colleague and ask for help.
Boxer also links with Dropbox for file sharing, and syncs up with LinkedIn and Facebook to give your contacts profile cards. Boxer is currently free and works with Exchange, Gmail, Yahoo Mail, Apple's iCloud, AOL Mail and Microsoft's Hotmail.