Here are the two best Centrino utilities that I have found in order of preference:
1.
Centrino Hardware Control - Full featured program that has a little bit of a foot print. Monitors all sorts of temperatures and voltages as well as just changing speed preferences. HIGHLY RECOMMENDED!
2.
Speedswitch XP - Lightweight program that just does basic power settings and speed monitoring. The speeds are not always accurate in my experience. I used this for a long time and switched to Centrino Hardware Control because of all the other useful things it could do.
Just wanted to put these very useful and critical tools out there for all to see.