The Directory of Open Access Journals (DOAJ) is going from strength to strength. DOAJ now lists 3756 journals. 1312 of these journals are searchable at article level, the number of articles included being 222745 as of today.
The goal of DOAJ “is to increase the visibility and ease of use of open access scientific and scholarly journals thereby promoting their increased usage and impact.” It “aims to be comprehensive and cover all open access scientific and scholarly journals that use a quality control system to guarantee the content.” More information about DOAJ is available at http://www.doaj.org/doaj?func=loadTempl&templ=about. There is also a page of FAQs.