Lilies are poisonous to cats

Tiny amounts can be deadly. All parts of the lily plant are considered toxic causing damage to cats' kidneys and death in about 5 days

Easter Lily - Lilium Longiflorum (picture by martius from flickr)

Lilium Tigrinum Tiger Lily (picture by KingsbraeGarden from flickr)

Lilium Tigrinum Tiger Lily (picture by sunship_98 from flickr)

Partialy list: Easter Lily - Lilium Longiflorum Lilium Tigrinum Tiger Lily Lilium Speciosum Rubrum Lily Japanese Show Lily - Lilium Lancifolium Day Lily - Hemerocallis Species

See:

Easter Lily Hazard For Cats