Two days ago I took a look at CloudMagic's Android email client, and I have to admit, it's a well-designed piece of software. Its blazing fast searching is its claim to fame, but even without this functionality, it's an attractive, holo-friendly app with support for multiple accounts and a unified inbox. But - and for many, this is a big but - the app indexes your mail on CloudMagic's servers.
If you're the corporate type and have had some issues with Android's default Exchange compatibility, then you've probably looked for a good alternative. Among the contenders is an app by NitroDesk called "Exchange By Touchdown," which allows for secure, encrypted Exchange synchronization.