Hopping on the history meme bandwagon
sesam@lillemor ~ $ uname -a
Linux lillemor 2.6.24-gentoo-r4 #1 SMP Tue Apr 8 12:07:37 JST 2008 x86_64 AMD Athlon(tm) 64 X2 Dual Core Processor 4200+ AuthenticAMD GNU/Linux
sesam@lillemor ~ $ history | awk '{a[$2]++}END{for(i in a){print a[i] " " i}}' | sort -rn | head
128 mplayer
49 startx
48 su
31 cd
30 mc
29 ls
17 sshfs
15 screen
14 df
11 rm