Bulbous irises cross only to other bulbous ones.
Among rhyzomatous irises bearded ones are compatible, but not with unbearded. Compatibility is variable among the later.
Species number and variability is very high in all three groups with tall and dwarf ones.

Many crosses done and much more to do.

The only bearded X non bearded ones that I have heard of are I. pallida (bearded) X I. tectorum (crested)
Hope that helps. There is a list specifically related to species iris, where crosses are discussed, and sometimes photos shown. If you e-mail me privately I will direct you there.
Cheers, Jan

Here's an old report on some interesting Iris hybrids.
http://www.bulbnrose.com/Heredity/irisbrd.htm

Christy Hensler of The Rock Garden is doing some of the most innovative Iris breeding that I know of.

Karl

Here is a link that might be useful: The Rock Garden

Since I posted the previous note I had to change my URL, so the link to the Iris hybrids is:
http://www.bulbnrose.org/Heredity/Iris/irisbrd.htm

Also, the link to Christy's page has changed. I'll link it below.

And I have a page of Iris information - old cultivars, breeding, etc.
http://www.bulbnrose.org/Heredity/Iris/Iris_info.html

Karl

Here is a link that might be useful: The Rock Garden