I have posted this before but seems like it came up in the news recently and I wanted all dog owners to know about it since this person saved their dog because someone else told them!
Certain types of sugar-free gum, mints, candies, toothpaste, chewable vitamins and throat lozenges contain the sugar alcohol sweetener Xylitol, which is used as a sugar subsitute. Xylitol is safe for people and felines, but when dogs consume Xylitol, they get a surge of insulin causing hypoglycemia. The sudden surge of insulin can also cause liver failure in dogs, depending on how much Xylitol is consumed.
http://www.9news.com/rss/story.aspx?storyid=195690