FAQ Search Tool

Hello everybody,

I am doing some research into FAQ search tools 'best practice' and
am struggling to find research material that covers this. Does
anybody know of any research that covers presenting FAQ's
alternatively by category and most popular and establishes which
method is more effective and in what situations this is the case?

Also would be great if anybody has any personal experiences and / or
opinions regarding this issue.

Please send links of any good FAQ search tools you can think of.

Thanks!

Daniel.