Windows Live Gallery
I have used this one since 7 came out. I heard about it from a CNET article that I can't find anymore.
First the pros: It shows the current clock rate (for notebooks). Color cued CPU/RAM usage monitors. Has the option for a calendar and multiple clocks.
Also shows battery level, battery plan, the signal strength of the wireless network you are connected to and even the uptime.
Clicking the monitors themselves gives useful info or opens relevant programs.
Examples: Clicking CPU monitor brings up task-manager, clicking the RAM monitor brings up performance-monitor. You can specify the calendar program of your choice for the calendar.)
The appearance is customizable and you can stack the monitors whatever way you like. Blah Blah time formats, GHz, MHz et cetera et cetera.
Now the cons:
Battery monitor has trouble with certain notebooks (Some Sonys, HPs, Lenovos and others).
The settings menu has a annoying lag time (prolly' cause it has to poll the OS for so much info, maybe?).
The settings menu just kinda sucks.
This is a side project for him, but he does listen to issues with the gadget.