In addition to the general databases listed under Articles in the Starting Research section, you should consult the following:
A good starting place for research is the MLA International Bibliography, which contains articles, book chapter and books on medieval English literature. You can use the MLA International Bibliography's search page to perform a keyword search, or to combine words and narrow your search down further. You can also limit your search results so that you're only looking at peer-reviewed sources, only full-text sources, or only sources that were published within a particular time range (among other search options).
Literature Criticism Online allows you to perform keyword searches, full text searches, and exact author searches, in the event that Literature Criticism Online has an article about your author.
In the "Criticism" sections of articles, Literature Criticism Online points to more print resources, such as journal articles, that you can track down to decide whether they'd be good to cite in your bibliography as well. Some of these articles are excerpted, and the full texts of some are included. Note that when you're citing articles that are excerpted or quoted in Literature Criticism Online, it is necessary to note in your bibliography that you viewed it through Literature Criticism online (unless you've actually tracked down the article in the periodical or publication in which it was originally printed).