Here are a few recent papers on counterpart theory:
In "Counterparts and Actuality", Michael Fara and Timothy Williamson argue that adding an actuality operator to CT is obligatory but it ruins the counterpart theorist's day.
In "The End of Counterpart Theory" Trenton Merricks argues that non-Lewisians who are counterpart theorists are in serious trouble. (This paper is unfortunately not available online but should be available via campus computing resources.)
In "Beyond the Humphrey Objection" Ted Sider responds to objections from Merricks and Fara and Williamson (as well as Kripke). This is an in-progress defense of counterpart theory from some of the most serious damaging recent objections.
Finally, I earlier linked to Delia Graff Fara's paper from the Second Online Philosophy Conference "Counterparts Within Actuality" (along with comments by Sider and Melia (the co-author of "Lewis's view is either not reductive or incomplete" argument from Divers chapter 7)). Counterpart theorists' days are again ruined.
(Most of this has fairly technical moments but mastery of the above material plus chapter 8 will make you up-to-the-minute on the philosophical debates over counterpart theory. As always, feel free to post questions/comments.)