Cosmos atrosanguineus, the "chocolate cosmos". It really does smell like dark chocolate, although faintly. The blooms are a deep brownish-maroon-black.

Great post! Black plants are yummy! (I have to say though that I grew aster liliput blue moon and was pretty disappointed... flowers were tiny and mostly pale lavender, not showing much of the dark color you see in the pictures...)
My personal favorites:
nemophila 'pennie black'
bachelor buttons 'black ball'
chocolate cosmos (well, suuuuuuuuuuper dark burgundy, but close!)
pelargonium sidoides (really cute!)
tulip 'queen of the night'
tall bearded iris 'superstition'
black peony flowered poppy
I'm sure I'll think of more later...
Amanda 'romando'

Black Flower Viola appears to re seed it self reasonably well in our garden. I can't say we have had much luck with Black Dianthus which I really adore.

Ankrara's Hobby Corner

Aeonium Zwartkop (photographed at East Ruston Old Vicarage in England)

I also liked, at this same garden, this black foliage plant which I'm guessing is a Phormium, but I don't really know (isn't this combination pleasantly sinister somehow?) :

I could go on and on -- black dahlias, black hollyhocks, black daylilies -- but here's what turned out to be a surprisingly great little annual in my garden this year, a black Salpiglossis:

They're adorable! I want!

I forgot to mention 'Black Dragon' and 'Chocolate Drop' coleus. I grow black dragon every year, it is great in containers. I just discovered chocolate drop this year, it is a trailing coleus (the two I bought last month were already about 3' long!) with litle green and chocolate leaves.

Phyllostachys nigra - Black Stem Bamboo. The leaves are green and make a stunning contrast to the truly black (well, very deepest charcoal) stems. Does well in container and I've had some luck growing inside although it's hardy here.

Ophiopogon planiscapus "Arabicus' is truly black but oh-so-slow-growing!

Coleus 'Blackberry Waffles' was described as looking like blackberry syrup in the Singing Springs catalog and it's an apt description. Also I like Coleus 'Dark Star'.

Off to check on Garden-witch's recommendation for Coleus'Black Dragon' and a few others mentioned ...thanks. josh

Here is a link that might be useful: Black-stem Bamboo

Like Josh, I recommend Ophiopogon - Black Mondo Grass. Here, it grows well, is winter-hardy (go figure- when I first acquired it, it was rated zone 7) and after the first or second year, spreads fairly quickly, though is never invasive.
I also like Anthriscus sylvestris 'Raven's Wing' which looks
similar to Queen Anne's Lace, except for the pretty, ferny, chocolate-brown, almost black foliage.
I also recommend Cimicifuga 'Black Beauty'.
I also really like Aster laterifolius 'The Prince' which sports congested black foliage and myriads of tiny white flowers with raspberry centres.
I'm also fond of Hemerocallis 'Salieri' a great daylily with wonderful black flowers.
Perhaps the best black plant I saw this year was a fantastic ornamental cabbage or kale. The foliage was a deep midnight black. I'm not sure of the cultivar, but I've never seen anything quite like it.

Oh heavens, check out Black Magic and Purple Passion for 2750 dark plants, full descriptions, over 400 photos, USDA zones. Some of the names you have for plants are not correct. There is only one black mondo grass Ophiopogon planiscapus 'Nigrescens' all the others are selling names. This is my favourite black plant, because it is interesting all year round. Grow them all year, they deserve it, they are not 'witchy', although good fun for Halloween.
There is an International Black Plant Society too.

Here is a link that might be useful: black plants

A new one to add to my favorites: fava beans! Really! I went on a nature walk the other day and came across some stems of beautiful black and white pea flowers. I didn't know what they were, but 2 brilliant folks on the name that plant forum knew exactly what I was talking about! Google fava beans for an image; they're cool! A white pea flower with a truly black hood.

Amanda 'romando'

I love 'black' flowers and plants. The only ones I've grown are tulip'Queen of Night', Ipomea'Blackie' and some unamed black pansies.
I ordered some calla lilies'Black Forest',which I believe I bought as a cut flower. I also ordered iris 'Before The Storm'. I cant wait till they come.
The black mondo grass is really nice. The taro'Black Magic' too.
Viola'Bowles Black'.
I haven't grown it,but the foliage of canna'Wyoming' looks almost black, in the pictures anyway.

A florist is a person designing flower arrangements and selling them. The florists take care of flower arrangements, which is an art of making bouquets, composition of ornamental grass, herbs, foliages and flowers resulting in a beautiful design. Knowledge in complicated arrangements of flowers along with know-how on forming bouquets and wreaths is very important for a florist.

Here is a link that might be useful: Perth Florist