I've been using RMClock for almost a year now and it's great.

Just a small note for people that also want to go down the RMClock route, you do NOT need to have CnQ enable in the BIOS for it to work. I've confirmed that my CPU does indeed clock up and down successfully using a number of CPU speed reporting programs (eg CPU-z, ClockGen, CBid, CrystalCPU, Systool etc)