First of all I advise you to download the PMP Handbook under this link http://www.pmi.org/CareerDevelopment/Pages/MaintainYourCredential.aspx ) and read the CCR section.
In brief you have the following options:
You can obtain PDUs from any REP (Registered Education Provider) who can offer you training programs acknowledged by PMI. There are many REP’s who can offer you free courses or web seminars and grant you PDUs upon completion. You can get many PDUs through attending free web seminars offered regularly by the International Institute for Learning ( http://www.iil.com/freeresources ). You can go now and start earning your PDUs.
Free PDU training cources:
One of the best options is to join a PMI chapter and get 1-2 PDUs per monthly meeting that you attend. Attending a Project World session can get you 30-40 PDUs per week.
Creating and presenting a training session related to Project Management will allow you to claim PDUs.
You can also receive 5 PDUs per year for being a practicing Project/Program Manager up to a total of ten PDUs (2-years). Volunteering with your local chapter can earn you 5-10 PDUs per year. And attendance at one of the PMI Global Congresses can earn you 20-40 PDUs depending on the number of sessions and tracks you attend.
There are many no or low cost ways to earn your PDUs, my advice though is do not fall into the trap of waiting until your last year and try to get them, you just end up spending tons of cash to stay certified. Set a goal of earning 20 or more per year.
There is a little known fact though that you can earn as many per year as you wish. Each time you obtain 60 PDUs you can submit them, I know many people whose PMPs expire 6-12 years in the future and I personally have 6-years on mine.
Three companies that offer some excellent webinars (some free others at small fee) that are 1 hour and offer 1 PDU.
Publishing articles is getting easier and easier every year. There are many physical and electronic newsletters that are starving for good stories. Even if you have never written anything for publication, write up a few-page story about a recent project, experience, or technique, and someone will publish it. Offer it to a few different on-line PM blogs, chapters, SIGs, and other groups, and you will quickly become a published author.
The PDUs are the smallest benefit of writing, speaking, and teaching. Most importantly, it improves your own knowledge tremendously. You can also build up a positive professional reputation very quickly this way.
www.ITMPI.org . They have wonderful webinars in content. You get 1 PDU per webinar.