atMonitor is the most advanced monitoring tool for Mac OS X that displays system activity in real-time. It is designed to allow quick assessment of computer's state and it is powerful enough to make it a core utility in anyone's system troubleshooting toolkit.
atMonitor offers a better alternative to Apple's own "Activity Monitor" and combines the best of the features of many other existing monitoring utilities. It also adds an extensive list of unique features of its own. In addition to the standard CPU, GPU, VRAM, FPS, Disk and Network info, atMonitor allows interaction with processes, setting up triggers, logging, purging RAM and much more. atMonitor can be displayed in the menu bar, as a stand alone floating window or in the dock icon.
The tool shows you the system usage in a nice sidebar as well as in the menubar similar to iStat.
it also keeps you informed about the 3 applications that draw most cpu power in one quick look.
In the process list you see all applications unlike the activity monitor that hides system services from you, this can be useful but as well dangerous if you dont want you are doing. Stuff like changing priorities of a process and sending unix signals is very handy as well.
Since its free its a definitive download recommendation, go grab it now!