I've only really developed marriage customs in my country Lukok, though I know that in Thomorai marriage partners traditionally pierce their ears. (So you could imagine how alarmed Thomoraiis would be to see young girls with pierced ears, or, even worse, multiple piercings!) Marriage ceremonies in Lukok are kind of...bloody.

The mother of the bride and father of the groom preside over the ceremony. First, the bride gives the groom a dagger and says "I give you all power of life and death over me," or in Lukokish, "Nïvet krödï, ekeşusönï ëäns nïenet kîesdï nïemönet kîesdï meve dikçë enêru." The groom responds, "I accept your gift of love in love," or "Enêleruemït jäenes kîesej meve dirê enêru kones kekeok." Then he gives the dagger to his father, who says, "People of Lukok and God of that which is known and that which is unknown, witness this gift," or "Meoï Lükok kîesëz, Keşun jäveleş kîesëz jänuveleş kîesëz, di veş veşre ärv enêleru." He then kills a small animal called a cashewt using this dagger, to seal the promise. Then the groom gives the bride another dagger with the same words, and she gives the same response, and gives it to her mother, who says the same words as the groom's father and kills another cashewt.
Finally the two parents join the couple's hands together and put blood from the two cashewts on them, and then another person brings a bowl of water and the couple washes each other's hands in it. After this the couple are considered married, and they usually have a celebration that's a bit more cheerful. When the bride and groom finally reach their house after all the celebrations, they splash the bowl of water they washed their hands in over the doorstep, saying, "People of Lukok and God of that which is known and that which is unknown, remember these gifts." Unfortunately, I never translated that line into Lukokish and my dictionary is in another country, but it would sound pretty much the same as what the parents say.
The idea there is that the couple is letting their parents, in arranging the marriage, kill a part of themselves (the cashewts) - their independence, their freedom, their right to their own life. But then the husband and wife will help and support each other, and so ease the weight of the power they have over each other (the handwashing). It's actually rather Christian now that I think about it; it sounds a bit like salvation.
Wedding ceremonies are fun because you can have a mixture of awesome symbolism, random customs and superstitions, and just fun ways to celebrate.

I'd love to hear about anyone else's! And, like everybody else, I love the Rylle ceremony.

I have heard about real-world cultures that stage a bride kidnapping for a wedding ceremony...that would also be fun to include!