On another forum I belong to I read a thread about a person's cat dieing from Lily pollen, though any part of the Lily plant can kill a cat.
Here's a site that lists some of the plants that can kill dogs;
Also note that chocolate and onions can kill a dog. In the UK they estimate that 150 dogs die every year around christmas because of chocolate.
Here is a list from Britishcats.co.uk;
Plants (and Trees) that are Poisonous to Cats
Amaryllis *Indicates those commonly found in the house:
Common or Cherry Laurel (Prunus Laurocherasus) *
Dumb canes (Dieffenbachia) *
Elephant's ears (Caladium) *
False Jerusalem Cherry (Solanum Capicastrum) *
Lily of the Valley
Poinsettia (Euphorbia Pulcherrima) *
Rhododendrons and Azaleas
True Ivies (Hedra) *
NOTE: This is not a complete list.