If you want to improve your overall market-ability in your current field, consider the several areas currently most valued by employers, according to experts in job training and development. Computer skills are vital, but general training is far more valuable than specialized courses geared to a particular niche. Perhaps you've never used a certain computer platform and you want to brush up your skills. You may want to consider a course that gives you a variety of many different programs that work on that platform, rather than one that focuses on a single program in depth.
Generalization is the key.
Other courses that add luster to your resume include those focusing on communication skills, training in the latest tactics for improving customer relations, and courses in general management. If you're trying to break into the management arena and you can't get the career development you need on the job, you might consider volunteering for management duties at a nonprofit organization. That kind of volunteer experience transfers well onto a resume and can give you the boost you need. If you're considering education that would lead to a career change, carefully look at what type of work would interest you most and tap into your natural abilities. Of course, demand is also an important factor.