Since the 2.1 update hit my Eris, I've been far more inclined to use widgets. As such, I thought that it might be interesting to start a thread solely about widgets to see which ones everyone here uses, as well as why they use them.
If you know right off hand, then try to include information about the available dimensions for each widget, measured in tiles. (In other words, since one home screen is a 4x4 grid, then a widget that takes up the entire with of the screen and half of its height is a 4x2 widget.) Also, please state which Android version you use, preferably including your device model.
As I mentioned previously, I'm using an HTC Droid Eris that's running Android 2.1. Here are the widgets that I'm using at the moment...
WidgetBoard (4x3, 4x1, 2x1) - Okay, this is the ultimate news app, in my opinion. Download RSS WidgetBoards and choose from three different sizes of widgets to convert RSS feeds into widgets. It's certainly not perfect, as it doesn't seem to work with all RSS feed formats, but it's bound to work for some of the RSS feeds that you read on a regular basis.