In layman's terms, here's a brief stab at things:
Catholicism: holy authority descends from St. Peter through the line of popes, then down through the church hierarchy. In order to be saved, intercession by this hierarchy is necessary, as is following various precepts like baptism, confession, etc.
Where Protestantism broke off from this is the intercession part - Martin Luther objected to the idea that you needed an intercessor between you and Jesus/God in order to be saved.
I'm afraid I don't know much about the differences between most Protestant denominations, but I do know some about Mormonism. They believe that a further scripture (besides the Bible) was revealed by the angel Moroni to Joseph Smith. The story this angel told was that after his death and resurrection, Jesus Christ visited what would later become the United States, and Moroni told Joseph Smith to go find "Zion." Other things that were revealed in this new scripture were that those who are righteous (baptized in the Mormon faith and who behave themselves) will inherit their own planet after death, along with their wives (who can only cross over from outer darkness, see below, if their husband whispers their secret name across the veil) and that their spirit children will come back to inhabit bodies on Earth. Everyone who's not saved, I believe, goes to a place called "outer darkness" till the Angel Moroni blows his trumpet at the end of the world, and then I think they'll be judged.
Mormons, forgive me if I messed that up. It's all second-hand from Mormons I know.
Here's a page that might be helpful on the differences between protestant denominations:
<a href="http://www.religioustolerance.org/chr_divi1.htm">
http://www.religioustolerance.org/chr_divi1.htm</a>