Yes, I know about xylitol because my husband is a freak about making sure our dogs aren't anywhere near toxic substances. I bought some xylitol lollipops once for my son because xylitol is good for your teeth (it kills one of the main types of bacteria that cause cavities, which is why it's often inn chewing gum and toothpaste) and my husband would not allow the lollipops in our home. I had to go give them away.
There are lots of lists of things that are poisonous to dogs. Herre's a list from the HSUS
The following foods may be dangerous to your pet
Candy (particularly chocolate—which is toxic to dogs, cats, and ferrets—and any candy containing the toxic sweetener Xylitol)
Coffee (grounds, beans, and chocolate-covered espresso beans)
Gum (can cause blockages and sugar free gums may contain the toxic sweetener Xylitol)
Hops (used in home beer brewing)
Onions and onion powder
Potato leaves and stems (green parts)
Tea (because it contains caffeine)
Tomato leaves and stems (green parts)
Xylitol (artificial sweetener that is toxic to pets)
Some things are big no-nos like xylitol, chocolate, raisins and grapes, alcohol and coffee. Those are actually poisonous. Then there are things that are just likely to be choked on or create an intestinal blockage, like peach pits, dough, avocado pits, corn cobs, etc. Then there are things that are poisonous but the animal would have to eat a lot (or be a very small dog), like apple seeds. Not everything is super poisonous. Some items just stay on these lists because there isn't enough research to know whether it's safe or not. Example: tomatoes.
Also, fyi there is a hotline you can call if your pet gets into something you think might be poisonous. I used it when one of my dogs found and chewed up a bottle of multivitamins (as you may know, vitamin D is toxic to humans when consumed in high doses so I thought maybe the same for dogs - I was very sacred). Luckily my dog didn't consume enough to warrant a vet visit so the hotline saved me a lot of money and gave me peace of mind. The number is (888) 426-4435 and it's 24 hours 7 days a week. They charge a small fee.