CPU Monitor has been rolled into the new Activity Monitor (along with Process Viewer) in the Utilities folder. So many new tidbits in Activity Monitor, but one which really is useful is the pop-up choice for viewing 'All processes, hierarchical,' letting you see which process spawned which subprocess etc.
This was very useful in figuring out why my Epson Scanner wasn't being recognized by the Epson Scanner software I had installed. The reason for it was that Image Capture spawned off an 'Epson Scanner' sub-application (authored by Epson) which hogged the scanner all to itself. Courtesy of Activity Monitor, I saw that, killed the sub-application and then could use the scanner to its full capabilities using the stand-alone software from Epson or Vuescan.
[robg adds: I have to concur -- the new Activity Monitor takes the best of CPU Monitor, Process Viewer, and top and rolls them into one great tool. It really dawned on me today just how nice this app is -- I had to use Windows' Task Manager on a couple of occasions and found it quite difficult to figure out which process I wanted to kill. With Activity Monitor, it's usually visually simple to find the process you wish to kill.]