Fourth

the best way is to assign a generated, complex, password and not offer anyway to change it. the only person who can change it is you and you only change it to another generated one. encourage your users to memorize it and NOT write it down anywhere.

programmingnoob

if user is not allowed to change it, then thats not very user friendly....

but then all these things we have around... like yahoo, msn etc... they all allow users to change it, how do they manage it? i mean of course i can not manage it all on my own, but how do they do it?

Fourth

well, i was suggesting a hypothetical and admittedly unrealistic approach but it really is the most secure. given enough time a brute-force will EVENTUALLY solve a password.

to be secure you really just have to rely on your users to make smart passwords. yahoo and msn accounts are stolen all the time because users have easy passwords or freely give their info away. nothing you can do to guard against stupidity save taking all the control into your own hands.