iStat Menus
Used by 10 peoplebjango.com ↗

“iStat Menus for menu bar widgets like weather, laptop temperature, CPU usage, etc”
Devon Zuegel Interview, Writer, developer · via Uses This 
“I have a few gauges in my menu bar courtesy of iStat Menus.”
Mihai Parparita Interview, Software engineer · via Uses This 

“I also have the excellent iStat Menus installed so I can see the freaking date next to the time in the menu bar.”
John Siracusa Interview, Programmer, writer (Ars Technica) · via Uses This