Here are a few. This is for plants that don't mind the constant moisture, not those that like moisture but need to be well drained.

I am in zone 5. So these plants are considering that. I don't know what zone you are so they may not be hardy in your zone.

Hibiscus (Rose Mallow)
Lady's Mantle
Many of the irises, Japanese iris for one
Astilbe
Ligularia
Chelone (turtlehead)
Eupatorium (Joe-Pye weed)
Helenium
lilium canandense (American meadow lily)
Japanese primrose (candelabra type)
Rodgersia
Trollius

Andrea, what zone are you in?

Moss and ferns

Louisianna iris's work well too :) Check the bog forum.

Lavatera and water hemlock!

Any willow.....I love my Pussy Willows....they also look great in a vase to root!

Acorus gramineus 'variegatus' varigated sweet flag

OOOO Acorus gramminatus variegatus is really really pretty, pair it with Colocasia illustris and the white spotted callas, gorgeous!

From what I understand, ginger likes "heavy wet clay" and the catalog I saw that in said "yes, you read that right" lol

Holly

Cannas love boggy soil. Also Calla lillies.
Lobelia syphilitica
Lobelia cardinalis
Lysimachia

Check out some of the pond plant catalogues and you'll find many marginals, all of which do well in wet soils.

wanda

I have planted the following bog loving plants:

Colocasia (elephant ears)
Giant Callas
Cannas
Ligularia
Carex
Hibicus Coccineus
Primulas

Louisiana Iris
Japaanese Iris
Candelabra Primroses
Cannas
Trollius
Calla Lilies with large spotted leaves