1. Forums are a good way to find great content. While you are not allowed to copy there conversation, but you can learn a lot and tell it in your own words.
Visit www.warriorforum.com if you are interested in internet marketing ideas.
2. www.sitepoint.com is a brilliant site to find niche ideas or concepts.
3. Sites like http://ezinearticles.com and http://www.articlesbase.com are great sources for good written articles. But you have to take the articles as they are, with links and authors name and resource box at the end.
4. You can also buy quality content, good sources are: http://www.scriptlance.com www.elance.com and http://www.vworker.com (former RentACoder). Be aware that if you bit to low, you might get bad quality only, even stolen or copyrighted material. To avoid this use www.copyscape.com to check the material.
5. Private Label Rights articles are a good way to add usefull content too. You can buy them single, as a package or think about a membership and get PLR articles on a regular basis. But you have to rewrite the text a little to make it unique and add your favorite keywords. You can also take the articles as they are and add maybe some sentences at the beginning and the end, to make them more unique.
Have a look at: http://plrzone.net and http://www.constant-content.com for example.
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