The standards for choosing an open access journal should be the same as the standards you use for any journal. Think, Check, Submit is a good campaign to start with.
Use the check list to assess the journal
Only if you can answer ‘yes’ to the questions on the check list
One method of publishing open access materials is to find a journal that publshing all or some of its articles open access. This may be in the form of:
Increasing numbers of journals opt for some sort of open access poilicy; ask the journals you usually publish with what their policies are.
A second method of providing open access to your work is to archive your articles in an open access repository. Depending on the copyright contract you signed when you published your articles, you may be able to archive pre-prints (before editorial- or peer-review) or post-prints (final accepted version, but usually not the publsher's formatted version). Usually a link to the publshier's journal/article page is required, and is also good for verifying publication and peer-reviewed status. Check your copyright transfer contract carefully, and review the SPARC Author Rights site.
Another form of open access is Open Data repositories. Even if your article is not open access, or if you haven't published an article on the data at all, the data may still be valuable to other researchers. So far data is mostly available through institutional (university, agency, or association) repositories, but other repositories are forming. Journals may also provide links to data sources, and sometime hosting, if submitted with an article. Ask about data hosting when you submit articles for publcation.