Follow along with the video below to see how to install our site as a web app on your home screen.
Note: This feature may not be available in some browsers.
http://openhardwaremonitor.org/
Does the whole system incudsing GPU/anything with a tempreture sensor. Can add icons to tray for monitoring and plot graphs over time etc. and is very low memory usage.
MSI Afterburner is variant of Furmark that has overclocking, stability testing, and the temperature and fan monitoring stuff you're looking for. I have used it with a 7900GS and currently a 9600GT, and have no complaints. Many people in this community use it as well.
http://event.msi.com/vga/afterburner/download.htm