Gmail for Android is no doubt the best mailing client out there for the Android OS. Gmail has recently been updated to have some new features.
1. Save bandwidth and battery by only syncing priority mail
2. Use label notifications to mash up filters, labels, and ringtones
3. Remember ‘Show Pictures’ for senders
4. Turn off sticky message actions in landscape or all orientations
5. Better TalkBalk support for accessibility
6. Performance improvements
I like number 2 the most because you can now assign specific ringtones for specific labels, neat little feature so you know when you've got an urgent or important email.