Get the free trial of Camtasia 2. It only lasts 30 days, but whenever you want to record after the trial has expired, just go into your time preferences and set the date back to a time when the trial was active.
There are no good recording softwares for a mac if you are looking for free ones. If you really wanted to be big on youtube, you could afford a PC (You can get very capable and cheap ones starting at $300)
Thanks,
Powdski