Most of the "widgets" are borderline-useless, with a few exceptions:
- Calendar - nothing like always having a small calendar on your desk
- Weather - Complete with the forecast, its the next best thing to being outside
- Wireless Network Status - a meter which shows the signal strength of your WiFi connection
But perhaps the most useful one I have discovered is Knut August Johansen's iTunes Companion. This one stands out above the rest, as it truly automates a tedious task - it fetches album artwork & details from Amazon.com and imports it into iTunes for your existing songs. It will also optionally fetch the Album name, Year, and Track Number and import that into iTunes as well.
I've thrown a number of songs at it - from ABC to ZZ Top - and it seemed to work a good 95% of the time. Simply amazing!