Nowadays most modern computer systems contain many hardware sensors capable of measuring current system temperatures, voltages and fan speeds. Often manufacturers install their own software solutions which are not standardized or lack additional features. But there are alternatives.

WebTemp reads out values which have been measured by free hardware monitoring tools such as SpeedFan, logs and processes them. WebTemp displays this data in nice statistics which can be automatically uploaded as image files to any FTP server in order to remotely monitor your system.
"Light" and banner displays are very popular and used in hardware community forums as live avatars and in signatures.