dawkins:release-33 simon$ history|awk '{a[$2]++} END{for(i in a){printf "%5d\t%s\n",a[i],i}}'|sort -rn|head
  232	svn
   29	cd
   25	sudo
   22	svnlog
   18	rm
   17	ls
   15	ssh
   12	notify
   11	python
   10	mate

Update: I like Tom's; cowsay, brilliant.