Well, although they are not technically green, Artemesia is one of my staples. Another Favorite is the leaves of the vine known as Cardinal Climber. They look like a Palm. I love all the Ferns when dried too.
Gardninlady

Leaves of scented geraniums are versatile. They hold up well and come in many shapes and sizes. While I don't think the lime-scented variety is particularly attractive as a growing specimen, the leaves, when dried, are kinda "freaky" (in a good way).

Oh, I thought of another one that I use as a staple...Gingko Biloba leaves. They make a great background for any other pressed flower arrangemnts

I like carrot tops,the leaves of smaller leaf hostas, and one of my favorite is something my aunt calls penny grass. It grows prolificly for her, but she is in zone five and I am in zone 4. She gave me a start and it is enough , but dwindles some years.I mostly have done pressed flower cards and like the seed heads from blue grass also.

My collections lately: Almost any small new leaves before they harden & expand: Tiny little vine tendrils from Clematis. All parts of the Japanese Climbing Fern. New chartreuse foliage from Spirea Goldmound. New red crinkly Rose foliage. New purple foliage from Lorapetalum. Almost all-white leaves from variegated plants like Osmanthus heterophyllus and ivies. Also bits of my houseplants like Polyscias although it's almost impossible to press nicely...still, it's so frilly!

And "weeds" are wonderful...young bits of Equisetum, violets, creeping jenny, geranium leaves & seedpods...I'll never in this lifetime use all I gather but what fun! jo

I love using the red and bronze japanese maple leaves.