I personally love the Zimbra mobile interface, and was originally using it in my Firefox sidebar, but decided it would be fun to embed it in my iGoogle home page.
Step 1: Add the following gadget to iGoogle:
Personalize Your Homepage
Step 2: Edit the settings for the iframe gadget and use the following URL (note - this URL uses the new Zimbra mobile interface, which I think is super sexy, but if you prefer the old one, remove "?ui-1" from the URL):
Step 3: Enjoy!
You may want to play around with the height a little bit, I use 450px.