If you are going to be working in the medical field doing programming then having any type of medical certifications are going to be a huge boon to the company you work for (especially as a contractor--it gives them that warm and fuzzy feeling that you can be trusted), but I don't see it as a necessity, just being aware of the rules and regulations will be enough to keep you happily employed.
Check out this site from the HHS (Health and Human Services) department--they have a lot of information on medical record storage and the like.. I think you will find the bulk of your information here:
http://www1.cms.hhs.gov/home/regsguidance.asp
In addition to HIPPA though I would suggest that you do a lot of research on Sarbanes Oxley--this is a regulatory setup that was started after the big Enron scandal a few years back and deals a lot with data retention. Is great to know some of those answers when you get into highly volitile data storage.
http://en.wikipedia.org/wiki/Sarbanes%E2%80%93Oxley_Act
Lastly, since you work in medical billing--ask your supervisors for guidance and training. It shows your level of motivated, they may pay for it, AND they have the knowledge and experience to help you find the right type of training.
GL! And if you find more please let us know. Never know when we may need the same info!
Edit - Additional Information
Oklahoma Health Services HIPAA Site
http://www.ehow.com/about_5061174_hipaa-certification.html
Also, I am not sure which college or technical school is closest to you, but I would call around and ask about HIPAA certification courses. Any accredited university will be able to offer you the information you are looking for plus when you present the idea to your bosses it won't be some online training from Alaska (no offense Alaska!) but instead will be a local course that they can feel good about.