SpeedFan - Hardware monitor for Windows that can access digital temperature sensors located on several 2-wire SMBus Serial Bus. Can access voltages and fan speeds and control fan speeds. Includes technical articles and docs.
SysGauge - SysGuage is a responsive software utility that monitors the memory status, CPU usage, as well as network and disk activities of your system.
Open Hardware Monitor - Monitors temperature sensors, fan speeds, voltages, load and clock speeds, with optional graph.
Big Meter Pro - Big Meter Pro is a utility that monitors the disk and memory of your CPU.
smcFanControl - [Download] smcFanControl 2.
SSuite System Monitor - SSuite System Monitor is a completely portable and stand-alone application that monitors the RAM of your system, page file load, CPU usage, and the system power in real-time.