I also work 9-5 at a big corporation.  I take time to learn and keep up with the latest developments in the programming world while I'm on the clock.  This usually amounts to an hour or so every morning reading through my RSS reader.  I've found that supervisors tend to appreciate that kind of motivation and self improvement.  I'm sure there are places that would not appreciate this activity.  You may be able to conduct this kind of self-education on the clock anyway with no noticeable decrease in productivity.  Some people will see this as unethical, but it's likely that it will ultimately be a net win for your employer because of your increased output as a result of the knowledge.  Otherwise, you may want to look for a different job that is more friendly to your proactive view of education.