Garden expert Ann Lovejoy wrote in a May 23, 2002,
article in the Seattle Post-Intelligencer newspaper:
"Which flowers are the safest? The answer is twofold. First, no flower is safe to eat or use on or near food products unless it has been organically grown. This means no chemical herbicides or pesticides have been used on or around the plant. Rose fertilizers that contain systemic toxins are included in this category, as are any fertilizers of the weed-and-feed variety.
"This also means that edible flowers that are brought home from nurseries and garden centers are not safe to eat or use on or near food products unless they have been grown organically or sustainably (without toxins). ...
"Secondly, for some people, eating pollen can trigger allergies or even asthma. To be safe, remove the pollen-bearing parts of each edible flower (the pistils and stamens). The sepals or calyx also should be removed from all flowers except the viola-violet clan (pansies, Johnny- Jump-Ups, violets and violettas)."
Copyright 2002, Seattle Post-Intelligencer,
Reprinted by permission
That said, quite a number of flowers common to vegetable beds and ornamental borders are both lovely to look at and tasty to boot. Below you will find a list
Click Images to Enlarge 
Acacia Blossoms

African Violets

Almond Blossoms

Alyssum

Apple Blossoms

Baby's Breath (Gypsophila)

Baby's Tears

Bachelor Button petals

Banana Blossoms

Borage
Substitutes:
Nasturtiums, Violets, Rose Petals 
Boston Fern

Bougainvillea

Bromeliad Family

California Poppy

Camelia

Carnation

Chamomile

Chive Flowers (Chive Blossoms)

Christmas Cactus

Chrysanthemums

Clary
Substitutes:
Nasturtiums, Borage, Violets 
Dahlia

Daisy

Daylily

Dianthus

Dogwood

Easter lily

English Primroses

Forget-Me-Nots

Fuchsia

Gardenia

Geraniums -
Scented 
Hawaiin Ti Plant

Hibiscus

Hollyhock

Ice Plant

Impatiens

Indian Cress (Tropaeolum Majus)

Jamaica Sorrel (Jamaican Hibiscus)

Jasmine

Johnny Jump-Up
Substitutes:
Pansy, Violets 
Lavendar

Lemon Blossoms

Lilac

Lily Buds

Lily of the Nile

Maidenhair Fern

Marigolds

Mimosa Blossoms

Nasturtium
Substitutes:
Marigolds, Pansy 
Orange Blossom

Pansy

Peach Blossom

Petunia

Phlox

Plum Blossoms

***** Willow

Roselle

Roses
Substitutes:
Violets for crystalizing 
Snake Plant

SnapDragon

Squash blossoms

Tiger Lily

Velvet Plant - Purple

Viola

Violet
Substitutes:
Nasturtium, Borage, Pansy 
Zinnia