In 1993 Rabbi Mordechai Willig, a Rosh Yeshiva at YU and a member of the Beth Din of America, drafted a prenup for use at Jewish weddings to avoid future Aguna/Mesorevet Get problems. The agreement basically obligates the husband to pay a fixed sum of money to the wife as support upon receiving notice from her requesting it. This is intended to be used by the wife to encourage the giving of a get.
His version of the agreement has received the approval inter alios of Rabbis Ovadia Yosef, Gedalia Dov Schwartz, Hershel Schachter, Zalman Nechemiah Goldberg, Osher Weiss, Norman Lamm, Yitzchok Liebes, as well as the Rabbinical Council of America. (That's quite an impressive list!)
Much more information is available at their website: http://www.theprenup.org/
If this is indeed permissible, it sounds like a good idea to me.
Do some current Rabbis/groups find this agreement to be problematic? If so, why? Is there a different variation they would find acceptable?