If you are PMP certificated (Project Management Professional) you are aware that you have to earn at least 60 PDUs every three years in order to keep it valid. There are many posts on how you can do that (earn PDUs), but most of them I found are either paid or outdated. Therefore I will try to maintain a list with the free alternatives...
1) Earn up to 12 free PDUs by attending the IIL Project Management Day (IPM). This free event happens every year and it is always the first Thursday in November. It is free and once you watch the 27 videos that are available for 30 days, you can claim 12 PDUs (http://www.iil.com/).
2) Earn 30 free PDUs from PMPodcast (http://www.project-management-podcast.com/index.php/component/content/article/14-faqs/faq/50).
3) Mentor or organize Project Management trainings in your organization.
4) Find a volunteer opportunity on PMI website.
5) Earn 1 PDU from RMC University (http://u.rmcproject.com/forms/default.aspx)
6) Earn 2 PDUs from PM training online (http://www.pmtrainingonline.com/earn_pmp_pdus). Two free SkillSoft demos.
I will keep populating that list...If you have suggestions, let me know and I will include them.