Research institutes, marketing firms and others can be good sources of information. The Pew Internet and American Life Project is one example.
There are numerous sources of secondary marketing data - not all free. Try to identify trade associations or organizations and research centers with an interest related to your marketing problem. This page contains a few suggestions for finding demographic information.
Some sites will provide access to older studies and surveys for free but offer current data for members only. These organizations often release some data in news releases or in articles in news sources such as those found in LexisNexis Academic.
