[radmuzom]

Write a book.

While it appears to be an "activity" rather than a "skill", I believe it is a skill.

My recommendation is write on something which you know well; most probably in finance as you appear to be most experienced in this field. It will be even better if you can make it programming oriented, as there are a dearth of programming books specific to specialized domains.

1. Writing well is something which sets apart great technical people from the good technical people.

2. Writing is much more difficult than it sounds. It requires much more clarity of thought than when you are working. At work, some things may be obvious to you - only when you write about it do you think about the fundamentals of a domain.

3. Depending on your goals and the medium of publishing, it may teach you something else - like HTML or Latex, for example. It may also lead you to explore options for self-publishing a book, which can be a good skill later on.