Keeping your email completely private on your iPhone can be a bit tricky if you still want to retain useful timesavers like automatic login or support for multiple accounts. Secure Gmail is a simple tool that adds a passcode unlock to your Gmail accounts on iPhone to keep people from snooping around.
When you open up Secure Gmail, you'll prompted with a four-digit passcode or pattern to get access. Once unlocked you can swap between multiple accounts without having to type in your password each time. The app itself simply loads the traditional web mail client for Gmail, but the fact you can secure access without having to log out or retype passwords all the time is a handy feature. Secure Gmail is a $0.99; download in the iTunes App Store.
Secure Gmail [iTunes App Store]