Years ago I did one with searchenginecollege.com (advanced seo course) although thinking back on it I wouldn't waste my money. Experience and results mean more then some online certification.
This site, this forum can help you more then any seo course . Ask the right questions and read as much as you can
SEO changes so fast that by the time you have finished a course the knowledge is already out dated. You gotta keep learning all the time.