In principle there are two options available for scientist to make their publications freely available:

The Green Road: free accessibility via the secondary publication (Self-Archiving). Meanwhile, many publishers of traditional toll access journals have a policy in place allowing the authors of the articles published in their journals to make the pre-/postprint and in some cases even the publisher's version of the articles freely available via the website or the institutional repository of the institution with which the author is affiliated. This policy might include an embargo period. The use of this option does not involve any charges! The Max Planck Digital Library (MPDL) is operating eDoc, the central institutional repository of the Max Planck Society.

The Golden Road: free accessibility of the primary publication.This is achieved by either publishing an article in a genuine Open Access journal or a hybrid journal. In so-called hybrid journals only some articles are freely available whereas genuine Open Access journals have a policy to allow free access to all of their articles.

Frequently, in both cases a publication fee is charged from the author. More about Cost Transfer.

Read more about Open Access at the Max-Planck-Society.

Publishers with MPS-OA agreement

• BioMed Central
  Since 2004 Max Planck Society has an agreement with BioMed Central. BioMed Central is committed to its policy of providing free, full text access to all original research papers published in any of its 80+ online journals covering all areas of biology and medicine, and any journals that will be added over time.
  
  List of Open-Access-Journals

• Public Library of Science (PLoS)
  PLoS is a nonprofit organization of scientists and physicians committed to making the world's scientific and medical literature a freely available public resource. PLoS applies the Creative Commons Attribution License (CCAL) to all published articles. Under the CCAL, authors retain ownership of the copyright for their article, but allow anyone to download, reuse, reprint, modify, distribute, and/or copy articles in PLoS journals, so long as the original authors and source are cited. No permission is required from the authors or the publishers. Thus, the contents of the seven Open Access journals of PLoS are freely accessible for the reader worldwide via internet.
  
  List of Open-Access-Journals

• Springer Open
  SpringerOpen is Springer's new range of fully open access journals, which cover all disciplines within the science, technology, and medicine (STM) fields, giving authors in all areas of science the opportunity to publish open access.
  
  List of Open-Access-Journals
  

• Wiley Open Access
  Wiley Open Access is a new initiative from Wiley to drive quality peer-reviewed publishing with speed and efficiency through open access publication. The program of new, fully open access, journals launched in early 2011.
  
  List of Open-Access-Journals

Other OA-Journals

Directory of Open Access Journals
Directory of Open Access Repositories