8. TouchDown HD
Stuck using an Exchange server for your work-based email? TouchDown HD is a fully featured Android Exchange client that should meet your corporate security requirements.
TouchDown HD provides an Outlook-like experience on Android, with email, contacts, calendar, and tasks in a single-screen tabbed setup. The app has its own notifications and widgets, too, so even though you won't be using Android's native email services, you'll still be able to get many of the same benefits. It features S/MIME encryption for sending and receiving and also supports remote wipe and data encryption as well.
The main TouchDown HD app is free; after 30 days, you'll have to purchase a $20 license key in order to keep using it.