Tulips are toxic to cats, dogs, and horses, but the majority of the toxin is concentrated in the bulb. Amaryllis is toxic to cats, dogs, and horses too. I think many plants from the lily family are toxic for pets.
Most types of lilies are highly toxic to cats, so I'd just stay away from those flowers all together. Daffodils are also poisonous to our pets. This is really too bad because my wife really loves them.
I really like daffodils, too, but since I like to let our kitty go out into our garden on a leash, I don't plant them. I plant catnip for her, and she loves rolling around in the patch of it in the garden!