Encryption of offline mail, calendar, contacts data on Android
Encryption of saved data (the data on flash storage) is a feature of Android 4.0 and higher. The only non-4.0-device I am aware of that allows full flash storage encryption is the Lenovo Thinkpad Tablet.

Encryption of connection data (data that goes over the wire) was a big security concern in some Android versions. Google has released some updated versions of the affected Apps, but it's unkown if they where dispatched on every device. IIRC most fixes got into 2.3.5, but I can't find the source ATM - Googles disclosure policy is not so good. Here are some good resources about this topic:


The Insecurity of Google's ClientLogin Protocol
What Android sync'd data is encrypted?
Ungesicherte Einsichten (german) ("Unsecure Insights")