Rainmeter can put system monitors, news displays, and other widgets on your desktop. Its resource-usage widget in particular looks good and offers good info. That said, Rainmeter in its current form is meant mostly for techies.
The tool runs from the system tray. You'll need to right-click its systray icon and choose an option from the Configs menu to get started. The choices for system meters (under the Bar and System config menus) look good, and offer useful info such as CPU, memory and network usage, along with drive space monitors.
But other options feel unfinished. For instance, you can only choose from four cities for weather, and can't add your own. And if you right-click a displayed widget and choose Edit Settings, you'll see the raw options file displayed in Notepad without any clues as to what changes what.
If you want a good resource monitor utility and don't need much else, Rainmeter could be what you're after. But if you also want customizable weather or other widgets, you'll probably be better off going with Google Gadgets (available when you install the Google Desktop) or another widget program.