I know RivaTuner and Everest can, but I'm not sure about GPU-Z.
Here's how to do it with RivaTuner:
Hit the little button to the right of "Customize..." in the main screen, then select the last button in the row of buttons that pop up ("hardware monitoring"). Hit the "setup" button on the bottom right of the screen that comes up, and then select the value you want in the "data sources" section ("core temperature", for instance), and hit the setup button right below the list. There's options now to show it in the tray or in the OSD. Oh, and before you close the screen with the graphs, hit the red button at the bottom left of it ("enable background monitoring", if you don't turn this on, the display goes away once you close the graph window).
You can also set rivatuner to start when windows starts, in the "settings" tab of the main window.