The Salem Witch Trials of 1692 are one of the darkest periods in American colonial history but, as you say, still have an important social and cultural ramifications. Here are some points you might want to consider for your informative speech:

• The trials mark the end of Puritan-style thinking in the colonies and the triumph of more modern ideas that are based on reason and logic. Could you imagine, for example, spectral evidence being presented in a courtroom today or a major catastrophe being blamed on a devil?  
• The trials teach us an important lesson about creating scapegoats, i.e. people who are incorrectly blamed for some disaster or shared problem. Have a think about modern examples of scapegoats. You could also look at the treatment of communists after World War Two or the McMartin Preschool Trials of the 1980s.
• These trials created the modern notion of witches meeting in secret and dancing in forests at nights. This idea led to the development of the genre, American Wilderness Gothic, which can be seen in lots of films, like the Blair Witch Project, Legend of Sleepy Hollow and To Kill A Mockingbird.