This is a good repository of some of the more popular Buddha nonquotes making their rounds.
There is currently an epidemic of mistranslated quotes, oversimplified quotes, or outright fabrications. If one has a little familiarity with the Pali Canon, the blatantly false ones are very easy to identify. The simlified quotes I don't mind as much, but there is definitely enough quotable and inspirational Tipitaka quotes that there is no need for this (Some parts of the Tipitaka, such as the Udana, seem designed solely for the purpose of providing bite-sized quotables.)
I think that because Buddhism still has this "oooh mysterious and mystical" factor in many western minds, many quotes from new age writers, gestalt and cbt therapists, transcendentalist and romantic writers, and motivational speakers seem to find their way to the Buddha's mouth. The fact that these quotes are very rarely provided with a scriptural source (as opposed to, say, Jesus quotes) adds to the confusion. As it stands now, there are many general "feel good" quotes that people try to retrofit into the Buddha because of lack of historical knowledge and wishful thinking, even if they stand in stark contrast to what the Buddha actually taught.
I try, when I can, to point out false quotes in as gentle a way as possible when I see them to try and make things ever so slightly clearer.