Any research paper or series of papers by a single author or by a team of authors is deemed eligible if
- the paper was published in a recognized refereed journal no later than December 31, 2012;
- the main results were not published (in either preliminary or final form) in a journal or conference proceedings before January 1st, 2000.
Let me close with a message to the "volume B community". Perhaps the logic/semantics/programming languages community should think strategically, look at the most prominent journal papers meeting the eligibility requirements and drum up the strongest possible support for those. Feel free to look at your crystal ball and suggest candidates for nomination using comments to this post.
As the new president of the EATCS until ICALP 2014, I am taking a sabbatical from issuing nominations in order to avoid any possible conflict of interest.