Perfgraph is a CPU / memory / network / hardware monitor. It is implemented as an Explorer toolbar so it does not necessarily take up space from your desktop.

A quick overview of its features:

CPU utilization display for up to 8 cores
Memory utilization indicator
Network throughput monitoring via SNMP
Network performance & reliability monitoring by pinging remote hosts
Hardware monitoring
CPU temperatures
Chipset temperatures & fan speeds
HDD temperature
Gigabyte Odin PSU support (voltage, current, power, etc.)
Very lightweight: minimal CPU and memory utilization
Perfgraph will run on both x86 and x64 versions of Windows XP or later.