A big thing in web design right now is around user experience (UX). There are some certifications around human factors engineering and UX in general that your school may offer. But certification just teach you a framework and not all employers look at them. Having a robust portfolio that shows you considered the full user journey would help you more than a certification.
Some of the Web Design Certifications are
• Microsoft Developer Certifications
• Google Mobile Sites Certification
• Adobe Certified Expert (ACE)
• MCSD: Web Applications Solutions Developer
• W3 HTML5 Developer Certificate