Lots of foods contain Xylitol, and they are increasing, but some include low levels of the sweetener and may not be dangerous, I don't know.

Sville, the chemical theobromine which is present in chocolate is toxic to canids. In fact, curiously enough, theobromine and caffeine are being used by USDA/APHIS/WS in an attempt to develop a new coyote toxicant. Not going too well, as the yotes often puke the stuff up before it takes effect.

An additional note should be made about Xylitol. Canids love sweet stuff and they seem to like the stuff, so beware lest your dogs come into contact with it.

All canids are effected by Xylitol, by the way. So are some ungulates {cattle, goats, deer also I believe}.