From atPurpose Technologies:
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, but 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.