Some great gadgets have made my iGoogle homepage really cool and helpful:
1. Netvibes universal widgets ecosystem - the widgets developers are building for Netvibes are stronger, cleaner, and more interesting usually than what has come out on iGoogle itself. Now most of those widgets can be ported to iGoogle for use on your homepage, (they also work for just about every other widget platform around).
The most impressive widget might be the Facebook iPhone widget, which lets you navigate through the slick, compact iPhone interface for Facebook directly embeded in your iGoogle homepage.
The second is Twitter King, which is a comprehensive and clean twitter widget that lets you see twitter updates and send your own, as well as direct message, right within the interface.
2. Compound gadget built in the iGoogle interface lets you combine several gadgets that you use little but want available often. In my case I have gMail, Google docs, and Google Calendar all at in one gadget - I leave gMail live so I can see when I have new email, but then I have easy access to my calendar and my documents when I need to use one or the other (this is the type of combined interface that gMail should possibly have at some point).
All in all I have 11 widgets on the page in some fashion. I can read blog posts, listen to music, browse social networks, manage my communication, read the news, and more without leaving the iGoogle homepage at all.