Checkout this thread
[webmasterworld.com...]
You'll find the answer by the money bucket.
:)
Alternatively, perhaps you are intending to develop a site targetting a high traffic sector - in which case, that is a totally different ball game. Maybe you could be a bit more specific. :)
I'm sure that the highest CTR would be words such as $^&£$, &*£ ,($(# and (£(**$£*($, but you might not be allowed to advertise on them, and unless you are tricking people to a site with some sort of malware/trojian/virus or you otherwise do not care AT ALL what your visitors do after they arrive (in which case the QS will hit you or you will get banned or you might even face a visit from the police), I also cannot see what value such untargetted traffic could possibly hold for you.
And if you try to define landing pages just to cater to those words, with no real content, again, QS is likely to push up minimum bids or some other Google-swerve will make it expensive.
Rgds
Damon
The keyword tools are all readily available in Adwords, which should be able to guide you in the right direction. But really your clients to stand back and look at their own product/service and website, and base the adwords account around that.