Top

Some useful top-like tools:

top

yes, simply top!

atop/htop

clones more information on processes with atop htop is very handy because of its interactive mode

apachetop

apachetop shows informations on requests to you apache
it's data base is the access.log-file

-q keep URI-parameters (e.g. for php-script calls)

dnstop

greps all dnsqueries from the network-interface...

iftop

shows all network-connections

mytop

shows mysql-queries

powertop

shows power comsumption of processes