The Oxford Handbook of Eschatology edited by Jerry Walls (Oxford University Press, 2008) is an excellent interdisciplinary collection of articles on all things related to Eschatology by world class experts in the field. A prime example of this is the entry on "Purgatory" by Paul J. Griffiths.1 Griffiths treats us with a fair and balanced summary of the historical doctrine known as Purgatory, the pro's and con's, in short, the various issues surrounding this controversial Roman Catholic teaching and a superb bibliography on the subject. Highly recommend it for anyone preparing a paper on this subject.
1 I highly recommend Griffiths work on the theology of honesty and dishonesty, Lying. An Augustinian Theology of Duplicity (Brazos, 2004).