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.
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.
Speccy - Speccy - find the details of your computer's specs. Great for spotting issues or finding compatible upgrades. Download the latest version free.
Open Hardware Monitor - Monitors temperature sensors, fan speeds, voltages, load and clock speeds, with optional graph.
AIDA64 - AIDA64 is a system information, diagnostics and benchmarking solution for Windows PC.
Macs Fan Control - Macs Fan Control is an iMac, MacBook Pro, MacBook Air, Mac Mini and Mac Pro fan control that is the solution of two basic issues namely noise problems and overheating problems.