Per MLA, "et al" is OK for "three or more authors," so if there's just two, list 'em. (http://www.aresearchguide.com/9parenth.html)
In references, the standard rule is to list up to five authors in the following format:
Smith J, Canton EM. Weight-based
administration of dalteparin in obese
patients. Am J Health-Syst Pharm.
When you have 6 authors or more, then you truncate the list to the first three, and add "et al." Looks like this:
Hunter DJ, Hankinson SE Jr, Laden F,
et al. Plasma organochlorine levels
and the risk of breast cancer. N Engl
J Med. 1997;337(18):1253-1258.
The Latinate abbreviation "et al." is short for "et alii," which means, "and others," and always refers to people, not objects. So if you had two authors, adding "et al." would indicate that there were other authors - and since there are no other authors in this case, it is incorrect to use it.
Note the standard reference style is to list last name and first name initial only (sometimes second initial). If you have long names, this style generally keeps the matter under control. The most important, overarching principle in reference citations is to present them in a form that will always pull up the paper in a Google search.
The most-common form to do that is what is shown above. Any attempt to be cute, or apply some kind of personal logic to the reference citation will not serve the reader because Elsevier publishing, PubMed, the Library of Medicine, and similar will generally list papers as shown. The critical point is to lead the reader to the exact paper cited.