Though I'd shy away from billing yourself as a "thought leader" - one of the most cliched labels ever - there's something to be said for sharing your knowledge in a way that is helpful to others - and in a way that's advantageous to your career.
To do that, among the recommendations of Liz Strauss at Successful Blog are to hone in on one area of expertise to remain focused, to network online and in real life to find people who need your expertise and then to look for opportunities to share your knowledge through teaching, writing or speaking.
If your goal is to gain visibility to potential employers, however, this post at JobMob provides a solution: guest blogging on other sites. That's a good idea, along with the one to focus on blogs that target your specific audience, though you have to wonder about the advice to "write a darn good guest post." Well, duh!
This post at Avid Careerist, however, points out some pitfalls with blogging as a means to get a job. Among them: Unless you're a darn good writer or have a darn good editor, grammar and spelling errors could torpedo your chances. Of course, you could be one of those people who's too cool to worry about that, who writes in all lowercase, for example. But chances are your brilliance won't shine through if people are bogged down in your writing errors.
So writer Donna Svei suggests another tactic: commenting. She advises finding relevant posts and adding, short, quick, meaningful comments. Specifically, she advises researching the online reading list of your ideal hiring manager and displaying your insights there. (With proper grammar and spelling.) She suggests using a gravatar, which displays your photo next to your comment, signing your name and your vanity LinkedIn URL.
It's certainly worth a shot, and if nothing else, it will keep you well-read in your core field, which makes you more appealing to potential employers as well.