Don't mention it if you can help it. You don't have to point out your degree was online; a degree is a degree. The vast majority of employers will never even ask, and if your resume looks good and you ace your interview, why would they even care? Chances are, they won't. The only time you should bring it forward yourself is applying for a job while earning the degree. Telling them that, though you are a student, but your education and thus work hours are flexible gives you an edge over other students.
If it comes up, or you went to a school well known for being online, focus on what edge an online degree gives you over traditional schools. You can't get an online degree without learning time management and self motivation, two major qualities employers are looking for. Think of what you've learned and how it will benefit your employer.
One of the biggest worries employers have with online degrees is believing it will lead to poor social skills. Become the master of the interview process and prove them dead wrong. They won't have time to think your degree made your socialization suffer if you interact with them professionally and with confidence.
Your online degree has required you to work with computers often. This is another bonus to the work force, since you will likely already have many bonus skills working with technology and software. Knowing your way around a computer makes many jobs easier today. Don't be afraid to put your familiarity with things like MSWord or Excel on your resume-- they're not skills everyone can claim.