You're probably aware of it, but anyway... Put

    HISTCONTROL='ignoreboth:erasedups'

In your .bashrc - now duplicate commands (two consecutive commands that were the same) are not included in HISTFILE, and also if you type " some-sensitive-command username password host" (note the extra space at the beginning), they too won't be include in HISTFILE.

http://serverfault.com/q/48769

http://serverfault.com/q/241154