Hats to wear.. (software I joke)
There could also be some Grey Hats, these may work in the short term but along with Black Hat users they could get sites blocked from being listed.
Black, Grey and white hats:-
http://www.solutions.ukdots.com/adve...g_methods.html
Do other webmasters agree with the recommendations at the above site, which method work, which lost visitors in the longer run?