MonitorPlus

MonitorPlus download

It displays the CPU load factor and memory usage in the menu bar.
Download from the developer's website

Additional links

Purchase at itunes.apple.com for $1.99

Alternative apps

CPU Speed Accelerator
9.0
Increase the CPU being allocated to your foreground tools.
Memory Usage Getter
2.6
Program which graphically shows the memory.
CPU History
1.1
FREE
Application that graphs your current CPU usage.
CPU Usage
1.0
FREE
This application shows the current CPU usage in a floating square meter.
Launch! Usage Meter 5
FREE
Launch! Usage Meter displays usage statistics on the BigPond broadband network.