History meme
I've noticed several other people showing their most frequently used shell commands so here it is from a few of my systems.
One of my spamtraps that publishes all the data to a webpage at http://www.spameatingmonkey.net :
selfishman@spamtrap:~$ history|awk '{a[$2]++} END{for(i in a){printf "%5d\t%s \n",a[i],i}}'|sort -rn|head
137 vi
46 ls
39 exit
29 /etc/init.d/qpsmtpd
27 cd
25 dig
23 tail
23 sudo
16 mysql
13 ps
The system [...]