A very helpful list from Carla Emery's The Encyclopedia of Country Living that I use as a reference because I have a dog and small children in my household. I am going to link images of the more common plants that can show up in yards and gardens.

Aconite
American False Hellebore
Anemone (wind flower)
Angel's Trumpet
Arrowgrass
Azalea - All parts are dangerous
Baneberry - berries are poisonous
Black Locust - flower is edible
Bleeding Heart - leaves and roots
Bloodroot
Bouncing Bet
Butterfly Weed
Castor Oil Plant - one or two castor beans can be fatal to an adult
Celadine Poppy
Chokecherry - leaves and seeds are poisonous
Christmas Rose - seeds and all plant parts are poisonous
Cockle, Corn or Purple - All parts poisonous
Columbine - All parts of the plant are poisonous
Crocus - autumn bulbs are dangerous
Daffodil - if eaten bulbs can create GI issues
Daphne - eaten berries can cause death
Datura - (Angel's Trumpet)
Daylily - Roots are poisonous
Deadly Nightshade
Death Camas
Desert Rose
Dieffenbachia - burning and irritation of mouth and tongue, can cause swelling
Digitais - (foxglove)
Dutchman's Pipe - all parts poisonous
English Ivy
European Bittersweet
Foxglove - All parts are dangerous
Frangipani - poisonous sap
Garland Flower - poisonous berries
Hemlock - deadly poisonous
Horse Nettle
Hyacinth - eaten bulb creates GI illness, can be fatal
Iris - entire plant is poisonous
Jack in the Pulpit
Jessamine - berries are fatal
Jimson Weed
Larkspur (delphinium) - poisonous seeds and leaves
Larsonia
Laurel - all parts can be fatal
Leafy Spurge
Lily, Flame - all parts are poisonous
Lily, Glory - tubers are poisonous
Lily of the Valley - leaves and flowers affect the heartbeat, stomach and mind
Lobelia - poisonous
Lupine - all parts including seeds are poisonous
Marsh Marigold
Marvel of Peru - all parts poisonous
Matrimony Vine
Mayapple
Meadow Saffron
Mistletoe - berries can be fatal to children and adults
Monkshood- all parts, including roots are poisonous
Morning Glory - all parts poisonous
Mountain Laurel
Narcissus - Bulbs are poisonous
Oleander - leaves and branches are poisonous
Pennyroyal
Poinsetta - even one leaf can be fatal to a child
Poison Ivy
Poison Oak
Pokeweed
Poppy, Horned - roots are poisonous
Poppy, Iceland - all parts poisonous
Poppy, Somniferum - fruit and sap are poisonous
Privet
Rhododendron - all parts can be fatal
Rosary Pea - seeds can be fatal
St. Johnswort
Skunk Cabbage
Snowdrops
Solomon's Seal
Star of Bethlehem
Tobacco
Wisteria
Yew - berries and leaves are fatal

-Jess