Verizon Droid 2.x works great with Zimbra. Email is push-style. Calendar sync works great. Contacts work great and can be presented as a single view of contacts across the Zimbra account and multiple Gmail accounts.
Visual HOWTO
1) Click on "Settings"
2) Click on "Accounts & Sync"
3) Click on "Corporate"
4) Enter your Zimbra username and password then click "Next".
5) Remove the backslash ("\") that is automatically added to your username.
6) (Photo showing backslash removed)
7) Click "Next".
8) Accept the defaults and click "Next" again. You're done!