The Max Planck Society is at the vanguard of the Open Access movement, making scientific knowledge, and in particular scientific publications, generally available free of charge.
Here is some additional information on the subject:
open-access.net - basic information about Open Access
Open Access Publishing Central Agreements for Max Planck authors
Copyright and self archiving for your own publication Information about publishers' open access and self-archiving policies
DOAJ Open Access Resources Directory of Open Access Journals (DOAJ)
Open Access Journals with central APC payment List of electronic journals in which Max Planck authors can publish open access free of charge because the article processing charges (APCs) are supposed to be covered by central funds