Since 2008, a list of ten purported Jefferson quotations has been passed around via email and posted in many places on the Internet.  This list contains some genuine Jefferson quotations, some misquoted Jefferson quotations, some completely spurious quotations, and some that are mixture of genuine and spurious.  The quotations are listed below with comments regarding their authenticity.

1. "When we get piled upon one another in large cities, as in Europe, we shall become as corrupt as Europe."  This is a genuine quotation, although slightly altered from the original, which reads, "I think our governments will remain virtuous for many centuries; as long as they are chiefly agricultural; and this will be as long as there shall be vacant lands in any part of America. When they get piled upon one another in large cities, as in Europe, they will become corrupt as in Europe."^[1]
2. "The democracy will cease to exist when you take away from those who are willing to work and give to those who would not."  This quotation is entirely spurious.  See its article for more details.
3. "It is incumbent on every generation to pay its own debts as it goes. A principle which if acted on would save one-half the wars of the world." This quotation is genuine, from a letter to Antoine Louis Claude Destutt de Tracy of December 26, 1820: "it is incumbent on every generation to pay its own debts as it goes. a principle which, if acted on, wou [ld] save one half the wars of the world; and justifies, I think our present circumspection."^[2]
4. "I predict future happiness for Americans if they can prevent the government from wasting the labors of the people under the pretense of taking care of them." This is a genuine quotation, although slightly altered from the original.  See its article for more details.
5. "My reading of history convinces me that most bad government results from too much government."  This is actually a quotation by someone else, talking about Jefferson.  See this quotation's article for more details.   
6. "No free man shall ever be debarred the use of arms." This is from Jefferson's draft of the Virginia Constitution.
7. "The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government." This quotation is often appended to #6, but it is spurious.  See the link in #6 for details. 
8. "The tree of liberty must be refreshed from time to time with the blood of patriots and tyrants." This is a genuine Jefferson quotation; see its article for further context and citation. 
9. "To compel a man to subsidize with his taxes the propagation of ideas which he disbelieves and abhors is sinful and tyrannical." This quotation comes from Jefferson's Virginia Statute for Religious Freedom, although it is slightly misquoted.  The original reads, "...to compel a man to furnish contributions of money for the propagation of opinions which he disbelieves and abhors, is sinful and tyrannical..."
10. "I believe that banking institutions are more dangerous to our liberties than standing armies. If the American people ever allow private banks to control the issue of their currency, first by inflation, then by deflation, the banks and corporations that will grow up around the banks will deprive the people of all property until their children wake-up homeless on the continent their fathers conquered." Parts of this quotation may be paraphrases of Jefferson's writings, while other parts are entirely spurious.  See its article for more details.