Edit by Brothersoft: With 8 separate and highly configurable menu extras, iStat Menus will let you know exactly what’s going on inside your Mac.
CPU and Memory
Both CPU and Memory sections feature realtime graphs and a list of the top 5 resource hogs. CPU usage can be tracked by individual cores or with all cores combined, to save menubar space.
See the amount of used or free space for one drive in your menubar, with more detail for any number of drives only one click away. You can even filter what's shown, to hide drives you don't want to see.