Open Hardware Monitor - Monitors temperature sensors, fan speeds, voltages, load and clock speeds, with optional graph.
GPU-Z - GPU-Z is a lightweight system utility designed to provide vital information about your video card...
CPU-Z - CPU-Z is a freeware that gathers information on some of the main devices of your system : Processor name and number, codename, process, package, cache levels.
iStat Menus - "An advanced Mac system monitor for your menubar."
HWiNFO - Professional System Information and Diagnostics. Comprehensive Hardware Analysis, Monitoring and Reporting for Windows and DOS. FREEWARE. download. Advertisements.
HWMonitor - HWMonitor is a hardware monitoring program that reads PC systems main health sensors : voltages, temperatures, fans speed.