What is the ruling on ululations (zaghareed) at weddings? Are they forbidden or permissible, and what are the evidences for this from the Qur'an and Sunnah?

There is no text that prohibits ululation (zagharid). The basic ruling concerning a woman's voice is that it is not considered 'awrah (private, to be concealed), however, it becomes forbidden if it is arousing or causes temptation, such as by softening or thinning it. Therefore, ululation is not permissible in the presence of those who would derive pleasure from hearing it.