Provide mechanisms that recognize the value added to the community by contributors.
A common personal motivation is to be respected and acknowledged by peers. For some Wiki users, this may be a major influence on whether and how much they contribute.
Most Wikis work on a volunteer basis, where no one is paid for their contribution. For most users, adding information to the Wiki is not part of their job. But, to use a cliche, recognition is its own reward. Showing that people's work is appreciated may encourage them to contribute more.