I went ahead and made a system temperature monitor using SpeedFan, that will measure the temperatures of your GPU, HDD, ACPI, and CPU Cores. There is Black Glass, White, and a Hud.Vision styled one, after mepu's awesome Hud.Vision skin for Rainmeter, in Horizontal and Vertical orientations.[link]
NOTE: You must have SpeedFan installed and running on your computer (Vista users will have to run SpeedFan as an administrator to output all of the temperatures) and some configuration may be needed to get everything up and running correctly. Place in C://Program Files/Rainmeter/Skins/(Any skin of your choice)
I am working on making one that will output RivaTuner GPU clocks (shader,memory,core) -- so look for that soon.
Let me know what you think!
UPDATE: I forgot to include the SpeedFanPlugin.dll, so its now in the file. Place the SpeedFanPlugin.dll in C://Program Files/Rainmeter/Plugins
Works with both 32-Bit and 64-Bit versions of Vista.