Baptizing the dead
Over my lifetime I have probably baptized hundreds of dead people, but only recently have I had the opportunity to proxy for my own ancesters. It is a much better experiance to do this for people you are related to. I believe that this is one of the most fufilling ordinances of which the Ladder Day Saints participate in. There is a lot of charity in this as it takes much of the time and energy of a willing participant to gather data on a deceased relative and then take an all day outing to a temple that is usually in the nearest city.
According to the scriptures, everyone who has ever lived will be raised from the dead through the atoning sacrifice of Jesus Christ wether you are baptized or not. Afterwards everyone is Judged by Christ. There are places prepared for everyone, and all will not be raised to the same glory in the resurection. those differences will be congruent with the entering of oaths and covenants which one makes with the Lord and will also be decisive upon wether or not the individual lives up to those standards. This is why there should be much emphasis placed on the ordinance of Baptism which ordinance is my maine focus as of yet.
Even since the begining, all of the dispensations of the Earth have been introduced to the ordinance of baptism. I think it is significant that in the history of Judaism there is what is described as Jewish ritual baths or (mikvah's) that resemble the baptismal ordinance. Much in the same way several old Testament regulations specify that full immersion in water is required to regain Ritual puerity after ritually impure incidents have occurred. Most forms of impurity can be nullified through Immersion in any natural collection of water. Some, such as a Zav, however require "living water," such as springs or groundwater wells. Living water has the further advantage of being able to purify even while flowing as opposed to rainwater which must be stationary in order to purify.
Here is a picture of a mikvah located in the Qumran sight where the dead sea scrolls were discovered.
Baptisms for the dead are a very sacred ordinance performed by Latterday Saints, it is treated as opening the door for those who never got the chance to hear the Gosple of Christ and a second chance to those who might not have accepted it during their lives. We do it for the welfare of those we love and because we believe in the resurection.