iMac Fan Control
For newer Macs, you might want to try Macs Fan Control (we use it ourselves on some of our newer systems).
Note: this item is free and unsupported and only works for certain, mostly older, Intel-based iMac models. There's also a MacBook/Pro Extended Fan Control version.
Download (includes source code)
Please: this item is free and unsupported — don't ask for support, other features, etc. — including about issues after uninstalling (see note below).
Note: The UI is sized for 10.5 so, given that 10.4 Preference Panels are not as wide, there's some truncation of the right side of the graph (i.e., when running under OS X 10.4/Tiger).
Although ugly and not intended (as stated in the notes, 10.4 wasn't tested), it's perfectly functional this way. If you're energetic and want to fix it, edit the NIB via Interface Builder, make the sliders shorter and move the graph to the left. Sorry, but I don't have any more time to spend on this.
Important: if uninstalling, you may need to reset the SMC per Apple's instructions.
Click on a graphic or a heading for a full-sized view.

