The activity monitor now doubles as a cpu monitor! You can right click on the activity monitor icon in the dock while it's running and choose the type of graph. For example Dock Icon -> Show CPU History or any of the others as shown in the screenshot.
[robg adds: Though it won't replace MenuMeters for me, it's nice to see these options available in an Apple-provided tool. As noted in another hint from late yesterday, Activity Monitor (i.e. Process Viewer) has really grown up with the release of Panther.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20031018145632624