Content is king, and a good blog makes for a great subject.
Blogs are one of the best ways to keep a buzz generated around your site, brand or product. With carefully selected keywords and thoughtfully written content, very targeted users will be visiting your blog. They'll comment, like and re-post your content around the web in various other blogospheres, social networks and special interest groups, thus giving your site a very high organic rank.
The benefits of maintaining a blog shows up almost immediately on search engines. You get more backlinks, higher recommendations and user generated content - things that are valued very highly when it comes to search engine optimization. Depending on your requirements, your blog can be technical, user oriented or talking about anything under the sun.