Tim Challies has a list of ways to be a Barnabas to bloggers. Here's one:
Send a Note of Encouragement. Short of leaving a comment, this is probably the easiest thing you can do. Simply find the person's email address or contact form and send them a brief note, mentioning that you enjoy reading their blog (and perhaps why you enjoy the blog) and encourage them to continue seeking the Lord.
Ken Hagler is great at this. He's sent me uplifting e-mails which as a blogger I find rather...well, uplifting and encouraging. It's an idea that works well in all other areas of life, too.
Hat tip: Joe Carter