one that iv seen used and favor towards is the good old "what are the x and y characters of your pasword" replaceing x and y with a number so for example:

Password: HostingDiscussion
Quesion "what is the 2nd and 6th letter of your password"
Answer "o and n"

It isent particually usefull if they cannot remember their password however the number can be changed dependant on the users password however 2 random letter chocies should be used where possible.

Works well on live support and via phone, both Norton, Orange, and O2 utalise the same quesion if not a variation of it.