On my various home screens...these have stood the test of time (several weeks, anyway...)
Android 2.1 News and Weather - Displays weather, news, or news and weather. I use it in News mode, shows news stories headlines, tap to open and have access to full range of stories. Add your own categories...very simple yet very cool. Only thing missing for me is zoom when reading stories (small print!).
CalWidget - clean and simple display of Google and Exchange calendar, many sizes available. Shows one or more days worth of events (depends on how full your calendar is and what size widget you choose). Great for a quick view at your current/next days' appointments...really can't imagine not having this available.
MoreIcons - allows you to double, triple, and "fourple" up the number of apps per icon on your home screen. I've assigned two programs to several icons - e.g., top 1/2 of one icon space is Gmail, bottom half is Email. Great feature to save space on your home screen, easy to use.
Network Widget - tells you the current network status of your phone, shows whether you're connected to VZW or to a wireless network. Seems simple, but it's quite nice to have confirmation on your home screen that you're connected (or not) to a wireless network w/out having to go view wireless settings.
Conversation - Only available w/the GDE home replacement app. Shows entries for recent phone/SMS activities in scrollable list (normal widgets don't scroll - GDE enhancement). You can select items to contact person. Really cool and really useful to follow-up on recent conversations.
MountUSB - Single click on icon on home screen to mount/unmount SD card when connected via USB. Allows you to use your SD card on your phone when connected via USB.
Beautiful Home (part of Beautiful Widgets) - Still using the last pre-Cease & Desist version, flip clock w/weather. As the name says, beautiful (and functional!). Love it.
Built-in Facebook widget - I know some people are negative on this one, but it works for me, simple and easy to use.
Built-in Music player widget - same as on the Facebook widget.
Aldiko - More a shortcut than a widget - allows you to place a shortcut to an eBook on your home page. Remembers your page, you can drop in and out the book at will from your home screen.
Ring Toggle - Not really a widget, but it's a key icon on my home page. One click allows you to set all sounds/notifications to both sound/vibrate, sound, vibrate, or silent/no vibrate.