Let's say you (or your company) have an amount of money that you would like to invest in improving your career, and probably make more money in the long run by landing a better job or raising your productivity. There are some classical investments that anyone would suggest:

• spend on programming books, since they pay for themselves very quickly;
• buy a better chair, since you will stay on that all day;
• attend conferences to improve your network of contacts.

I'm looking for more examples to weigh my options in the quest for improvement.

Google does not help as it only shows job ads for programmers in the financial sector.