I switched laptops recently, so I'm not sure how accurate this is, but here goes anyway:
$ history|awk '{a[$2]++ } END{for(i in a){print a[i] " " i}}'|sort -rn|head
143 ~/Apps/Firefox.app/Contents/MacOS/firefox
85 ls
57 cd
53 hg
40 rm
20 ssh
10 mv
10 ln
8 less
8 grep
Update: Fixed up the newlines. The meme came to me from planet.gnome.org, for any who are curious :)