I'm looking for non-standard answers.
Contributing to OSS projects and posting on StackOverflow are obvious.
I'm thinking more along the lines of volunteering to judge a high school programming contest.
I made this a community-wiki because I don't want people viewing or answering this question through the lens of reputation gained/lost. If you have a good idea, maybe you can inspire someone else to give back. if you want to give back to your trade's community and don't know how, hopefully this will help you out.
The goal here is to improve the level of interest in programming in a younger generation.