Terminal top command

from a suggestion somewhere (mailing list? web page? I forget)
in OS X (Panther, and other), open terminal and type:

top -u -F -R -s 3 -n15

Updated to explain variables
per request, (which you can get via 'man top' command)
-u = Deprecated, equivalent to -ocpu -Otime

-F =Do not calculate statistics on shared libraries, also known as frameworks. This substantially reduces the amount of processor time top consumes.

-R = Do not traverse and report the memory object map for each process. This substantially reduces the amount of processor time top consumes.

-s + integer "delay" = Set the delay between updates to "delay" seconds. The default delay between updates is 1 second.

n + integer "nprocs"= Only display up to "nprocs" processes. "nprocs" can be specified as the last command line argument without the -n flag preceding it. However, doing so is deprecated command line usage.