I just discovered htop a more colorful version of top. It loads faster and visually shows you how each CPU core is doing. Love it.

To install on the Mac

sudo port install htop

To install on Amazon EC2

64 bit:

wget http://pkgs.repoforge.org/htop/htop-0.9-1.el5.rf.x86_64.rpm
sudo rpm -Uvh htop-0.9-1.el5.rf.x86_64.rpm
rm htop-0.9-1.el5.rf.x86_64.rpm


wget http://pkgs.repoforge.org/htop/htop-0.9-1.el5.rf.i386.rpm
sudo rpm -Uvh htop-0.9-1.el5.rf.i386.rpm
rm htop-0.9-1.el5.rf.i386.rpm

Related links:
How to install htop in RHEL Centos or Fedora
Comparison between htop and top