A blog is all about discussion. Sure, your readers can discuss your article in the comments, but they can't submit any ideas except by sending you an email.
A great way to make your visitors visit your blog again is to integrate a forum, so that they can have discussions—with you and other visitors about various topics.
Forums don't work for any kind of blog. For example, I launched a forum on my blog www.wprecipes.com and it is pretty busy. I launched the same forum on www.psdrecipes.com, but this one is absolutely empty! It depends of your blog topic and your visitors. A great way to make people post on your forum is to give free help and advice.
Many solutions are available to integrate a forum on your WordPress blog: PhpBB/Vbulletin integration, BBPress, and so on. In my opinion, the easiest, and best, forum solution for WordPress is definitely the WP-Forum plugin. This plugin is complete, powerful and easy to install, use and manage...