There are several ways in which the OA and Wikimedia communities could interact. Let me just give seven:

1. Improving Wikipedia articles related to OA. A list of such topics for the English Wikipedia sits at http://en.wikipedia.org/wiki/Wikipedia:GLAM/OA/Catalogue. There are Wikipedias in over 200 languages, and all of them could do with improvements in this area.
2. Reusing OA materials in articles at Wikipedia and its sister projects. Examples of such reuse are given at http://species-id.net/wiki/User:Daniel_Mietchen/Talks/Open-Access-T....
3. Wikimedia Commons has a Picture of the Day competition at http://commons.wikimedia.org/wiki/Commons:Picture_of_the_day. There is also http://commons.wikimedia.org/wiki/Commons:Media_of_the_day and http://commons.wikimedia.org/wiki/Commons:Picture_of_the_year. For all of these, materials from suitably licensed OA sources are eligible (Wikimedia uses a CC BY-SA license, so materials licensed with -NC or -ND clauses are ineligible), and there is no principle problem with having an "OA image of the day" along those lines.
4. Similarly, there is a "Did You Know" project that features interesting bits of information on the Homepage of the English Wikipedia: http://en.wikipedia.org/wiki/Wikipedia:Did_you_know. Why not try to highlight some bits of OA this way?
5. The Wikimedia Foundation has drafted an OA and open data policy, which could benefit from feedback from the OA community: http://meta.wikimedia.org/wiki/Research:Committee/Areas_of_interest....
6. Some journals have teamed up with Wikipedia or are considering to do so: http://en.wikipedia.org/w/index.php?title=Wikipedia:Wikipedia_Signp.... Others are invited to join these experiments.
7. If there are suitably licensed materials from OA activities beyond publishing and self-archiving (e.g. from OA Week), they may well find a home at Wikimedia Commons too. An example is at http://commons.wikimedia.org/wiki/File:Open_research.ogg.

I am currently running a project that tries to facilitate all of these interactions ( http://meta.wikimedia.org/wiki/Wikimedian_in_Residence_on_Open_Science ), so I am very interested in anyone trying any of the above, and if you run into problems while doing so, I am prepared to help.