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