On my PC's, I am a big fan of Yahoo Widget Engine; heck, at home I have an entire 2nd monitor devoted to 'em. Unless you want to get OS specific (Mac OSX Dashboard or Vista Sidebar), there are really only two Widget choices to use: Yahoo Widget Engine or Google Desktop Gadgets. Soon, I'll do a head to head review, and give you my feedback. I'll let you know I run both at home. :-)
Check out this amazingly cool YWE widget, Neon Gauges :: System Info. It's every gauge you ever wanted, with slick neon reflection graphics, and smooth animation. Best of all, it's multiple widgets in one. Want to monitor the hard drive? Right click, and add it. Your battery? Right click.
Best YWE Widget I have seen in a while, and adds energy, style, and functionality to any desktop.