I would not send him to a website. They all have their strengths and weaknesses, and I think it is better to not let him surf on his own. If he ever does ask anyone else for their input, that other person will find the most contoversial statement and discredit the whole pro-polygyny position based on one line or statement. This happened to us with the Righteous Warriors site. Great site, but if the newbie or the newbie's mom or sister get a hold on the intimacy section, he will be drawn and quartered.
It is hard for me to think of anything better than the paper written by QMC05 on the links page, the objections page on this site, and then Tom Shipley's book, in that order. The first paper gives an historical and world view of polygamy and where it is used, and gives a new student the abiblity to see that it has been in place, is used today, and is not so abnormal as we think, and it is superbly written in a clear and non-cumbersome way. It is also not long winded. Once he has the open mind that is needed to study without prejudice, he will probably (hopefully) go to the Word and study for himself and maybe even ask advice from someone he respects. At this point, the biblical objections answered on the resources page would be a good study tool for him. Once he realizes that most pastors and mentors cannot refute the Word when it comes to this issue, he will need Tom's book to counter the much too common "last ditch efforts" of this biblical topic, which are the "not God's best, He just tolerated it, He just winked at it, we are free from the Law, that was Moses, God did not approve of that, those guys were just primal, we are much more smart and Holy" statements.
I would avoid James Stivers' book unless you take out the last part about polygamy saving the white race. It tends to offend people to the point that they discount the writing completely. All of the above can be printed to pdf and emailed, or printed hardcopy and handed over.
For what it is worth.
Paul