Free and unsupported from 

MacBook & MacBook Pro
Extended Fan Control

Download (includes source code)       iMac Version

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. Note: if uninstalling, you'll likely need to reset the SMC as per the instructions in this forum posting.