CPU tuner gives you control over the power consumption of your Android device. Its prime purpose is to save as much battery as possible, but it can be used to overclock at the same time (if the kernel of your device supports it).
Droid Overclock allows full customization of CPU frequencies and adds a ton of extras to your rooted experience. You can overclock to increase speeds or underclock to save battery life. Set custom profiles to increase performance to the max.