Lilies (broad sense)

Nearly all are six-'petalled' flowers (actually three petals and three sepals), often bell-shaped (actually placed in several different families):
Amaryllidaceae for Agapanthus, Allium, Amaryllis, Crinum, Galanthus, Leucojum, Narcissus, Nothoscordum, Sternbergia, Tetrastagma, Tristagma
Asparagaceae for Agave, Asparagus, Camassia, Convallaria, Cordyline, Hyacinthoides, Hyacinthus, Muscari, Ornithogalum, Polygonatum, Ruscus, Scilla, Yucca
Colchicaceae for Colchicum
Commelinaceae for Commelina and Tradescantia
Iridaceae for Crocosmia, Crocus, Gladiolus, Iris, Romulea, Sisyrinchium,
Liliaceae for Erythronium, Fritillaria, Gagea, Lilium, Tulipa
Melanthiaceae for Herb Paris and Veratrum
Nartheciaceae for Narthecium
Tofieldiaceae for Tofieldia
Xanthorrhoeaceae for Kniphofia

Choose by flower colour:

Blue/Mauve
Red/Pink
White
Yellow-green

'Lilies' - blue, mauve or purple

Hyacinthoides
Muscari
Hyacinthus
Crocus tommasinianus
Bluebells
Grape-hyacinth
Hyacinth
Crocus

Camassia leichtlinii
Romulea columnae
Iris
Sisyrinchium bermudiana
Camassia leichtlinii
Sand Crocus
Iris
Blue-eyed-grass

Scilla autumnalis
Scilla verna
Scilla siberica
Scilla peruviana
Autumn Squill
Spring Squill
Blue Squill
Portuguese Squill

Scilla forbesii
Colchicum autumnale
Crocus
Agapanthus
Chionodoxa
Colchicum
Crocus
Agapanthus

Puschkinia
Striped Squill

'Lilies' - pink or red

Erythronium
Lilium martagon
Fritillaria
Fritillaria
Dog's-tooth Violet
Martagon Lily
Snake's-head Fritillary
Snake's-head Fritillary

Allium
Gladiolus communis
Kniphofia
Crinum
Alliums
Gladiolus
Red-hot-poker
Cape Lily

Amaryllis
Nerine
Crocosmia
Tulipa
Jersey Lily
Guernsey Lily
Crocosmia
Tulipa

Watsonia
Romulea
Bugle Lily

'Lilies' - white

Allium
Ornithogalum umbellatum
Tristagma uniflorum
Yucca
Garlics
Garden Star-of-Bethlehem
Ipheon
Yucca

Galanthus nivalis
Leucojum aestivum
Polygonatum multiflorum
Convallaria majalis
Snowdrop
Summer Snowflake
Solomon's-seal
Lily-of-the-valley

Cordyline australis
Gladiolus callianthus
Hyacinthoides hispanica??
Narcissus poeticus
Cabbage-palm
Abyssinian Gladiolus
Spanish Bluebell?
Pheasant's-eye

Puschkinia
Erythronium
Gagea
Tulipa
Striped Squill
Dog's-tooth Violet
Snowdon Lily
Turkestan Tulip

Lilium candidum
Madonna Lily

'Lilies' - Orange, yellow or green

Gagea lutea
Narthecium ossifragum
Tofieldia pusilla
Ruscus aculeatus
Yellow Star-of-bethlehem
Bog Asphodel
Scottish Asphodel
Butcher's-broom

Narcissus pseudonarcissus
Narcissus bulbocodium
Narcissus jonquilla
Paris quadrifolia
Daffodil
Hooped Petticoat
Jonquil
Herb-Paris

Iris pseudacorus
Crocus crysanthus
Sternbergia
Asparagus officinalis
Flag Iris
Crocus
Winter Daffodil
Asparagus-fern

L. pyrenaicum
Alstroemeria
Kniphofia
Montbretia
Pyrenean Lily
Peruvian Lily
Red-hot-poker
Montbretia

Watsonia
Sisyrinchium
Bugle Lily
Pale Yellow-eyed-grass