Hi - there are all listed here - and I'm sure elsewhere as well: http://www.dahliaworld.co.uk/dahlia.htm

[ single ] [ anemone ] [ collerette ] [ paeony ] [ decorative ] [ ball ] [ pompon ] [ cactus ] [ semi-cactus ] [ miscellaneous ] [ waterllily ] [ fims ]. A very interesting site which I just found thanks to your question!

Anna

Here is a link that might be useful: Dahlia Types

And here are the Americanized versions of those forms.

Here is a link that might be useful: American Dahlia types

I saved that page for reference and then just now found out the linkd are no longer active! That means no pictures of the different forms!

Yes, that's a problem at that page, sorry I forgot to mention that. You can always google "dahlia anemone" or "dahlia Formal Decorative" etc and probably get to a page that shows them. I bet other individual dahlia societies have a working photo link.