According to About.com, one of the principal arguments against the Bill of Rights was that the government would be free to ignore rights not specifically mentioned in the document. The Ninth Amendment explicitly refutes that interpretation.
The text of the Ninth Amendment has historically been among the most difficult for the courts to interpret. By claiming that citizens have rights beyond those named in the Constitution, but declining to specify them, the Ninth Amendment left a very large area open for future court precedent to establish. About.com cites Griswold vs. Connecticut (1965) as one of the more high-profile exercises in Ninth Amendment jurisprudence, as this case established a "right to privacy" that was previously only implicit in the Bill of Rights.
According to About.com, other implicit rights found under the Ninth Amendment include the right to vote, the right to a fair trial, the right to be tried by a jury of one's peers, the presumption of innocence, the right to travel unimpeded, the right to procreate and the right to marry unless the state can demonstrate a compelling interest against it. About.com also lists the principle of judicial review as being among the unenumerated provisos of the Ninth Amendment.