Read over what they have to say - they may trigger some of your own ideas. Jot down notes while you're surfing the web. Every so often you'll find an interesting website or tidbit of information. Make note of the URL so that you can re-visit it and possibly use it in your newsletter. Visit a few message boards.
Message boards are a great source of first-hand information.
Read what others have to say, and take note of any interesting tips. Accept articles from others. Plenty of people are willing to provide you with free content in exchange for a small resource box that you would include at the end of their article. Keep up with the news. There are many sites that publish new items of interest to the Internet community.