SmartyPlants offers a nice selection of water lilies (Nymphaea), marginal/bog and floater plants.  The list of plants generally available include:

Arrowhead

Bloody Dock

Bog Lily

Canna Bengal Tiger

Canna Striped Beauty

Carex Floater

Cattail Graceful

Cattail Variegated

Clover, Variegated

Duckweed

Frogbit

Giant Reed VGTD

Golden Club

Hibiscus Burgundy

Horsetail

Horsetail Reed

Houttuynia Cameleon

Iris Blue
Iris Japanese

Iris Louisiana

Iris Red

Iris Yellow

Lemon Bacopa

Lobelia cardinalis

Lobelia Victoria 5"

Lotus

Ludwigia Sedioides

Mint Large Leaf Aquatic

Mint Small Leaf Aquatic FL

Nymphaea 'Bull's Eye'

Papyrus DWARF

Parrot's Feather Dwarf

Pennywort Variegated

Plantain Red 1g

Pot Pond 3g

Radican Marble Queen Float

Radican Marble Queen Pot

Rain Lily 1g

Rain Lily 5"

Rice Grass Ornamental 5"

Rush Blue Pickerel

Rush Corkscrew

Rush Horsetail

Rush Variegated

Sarracenia

Sensitive Large Leaf

Snowflake White Lg

Society Garlic VGTD

Spider Lily Variegated

Star Grass 1g

Sweet Flag

Sweetflag Variegated

Taro 5"

Taro Black Coral 1g

Taro Black Magic

Taro Elena

Taro 'Tea Cup'

Taro Violet Stem

Taro White Lava

Umbrella Palm 5"

Umbrella Palm Dwarf 

Umbrella Palm Regular

Water Calla 5"

Water Celery Variegated

Water Poppy Floater

Water Poppy Pot

Water Snowball

White Pickerel